Bosch C 1050 Manual
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6 720 644 894 Maintenance and service41 6 Maintenance and service 6.1 Annual maintenance (To remove front cover, see page 7.) Venting System • Venting system - inspect inside of flue pipe for a ny blockage or restriction. Observe burner flames during heater operation. (front cover must be removed). Inspect the combustion air inlet pipe for blockage or debris. Inspect combustion air and exhaust terminations for blockage or debris. Combustion Chamber • Inspect burner observation window (Fig. 77, #14) fo r cracks or spillage of flue gases. Observe burner flames during heater operation. Flames should be steady and blue with no signs of yellowing. Yellow burner flames are an indication of improper combustion. Refer to Section 3.4, page 24, chapter 3.3, page 10 of this manual to verify exhaus t system and combustion air supply meets manufacturers specifications. Pressure Relief • Manually open the pressure relief valve to ensure proper operation. Inlet Water Filter • Verify the inlet filter screen is clean and undama ged. The inlet water filter is located between the ¾ co ld water inlet fitting on the right side of the applia nce, and the water valve (See Fig. 33, page 29). Close installer supplied water shutoff, carefully lift th e water valve, then rotate back. Remove filter, clean and o r replace if damaged. Descaling • In areas where the water supply has a high mineral content, the heat exchanger should be flushed with a descaling solution. Scale build up will shorten the life of the water heater and damage resulting from scale is not covered under warranty. Refer to section 6.3 for detailed instructions on descaling the heat exchanger. Fin Coils • Inspect heat exchanger fincoil for soot build-up o r blockage. To access fincoil, consult service bullet in at www.boschpro.com . If there is evidence of soot build-up or blockage, the heat exchanger should be removed by a professsional and cleaned thoroughly. Condensate trap • Check water level in the condensate trap, see Fig. 35. • If appliance is out of service for more than 10 da ys, fill as described on page 31. • Check for debris and clean if needed. 6.2 Winterizing for seasonal use The water heater must not be installed in a locatio n where it may be exposed to freezing temperatures. I f the heater must be left in a space which is likely to experience freezing temperatures, all water must be drained from the heater. If precautions are not tak en, resulting damage will not be covered under the warranty. NOTE: Use of agents such as anti-freeze i s not permitted and voids the warranty, as they may c ause damage to the water heaters internal components. 1. Press ON/OFF switch on the water heater to turn OFF the heater and unplug power supply cord. The display should be blank. 2. Shut off gas supply to heater. 3. Shut off the water supply to the water heater usi ng installer supplied shutoff valve. 4. Open hot water taps to drain and relieve pressure from the plumbing system. If water continues to flo w after 5 minutes, a crossover of the hot and cold wa ter pipes is present and must be corrected before proceeding. Warning: Always shut off the electrical power supply, shut off the manual gas valve and shut off the water valves whenever servicing. Caution: B Check and clean the complete water heating system once a year. B Carry out a maintenance overhaul if necessary. Immediately repair defects to avoid damage to the system. Annual maintenance table Every year 1. Inspect venting system X 2. Inspect combustion chamber X 3. Inspect burner X 4. Inspect condensate trap X 5. Inspect water filter X Table 23 Annual maintenance
6 720 644 89442 Maintenance and service 5. Disconnect inlet and outlet water pipes from the water heater. Place a small bucket underneath the water heater to catch residual water remaining insi de the water heater. 6. Using an air compressor, blow short bursts of air (100psi max) through the inlet water connection unt il there is no water present coming through the outlet water connection of the heater. 7. Reconnect water fittings and return heater to ser vice when danger of freezing has passed. 6.3 Mineral scale build-up Periodic descaling may be necessary in areas with h igh mineral content in the water. Scale buildup in the heat exchanger may result in lower flow rates, error cod es of A7 and E9 and boiling sounds in the heat exchanger. A water softener is required if the water hardness exceeds 6 grains/gal (103 mg/l) calcium carbonate. Damage to the water heater resulting from hard wate r/ scale deposits will not be covered under warranty. Descaling using a pump 1. Disconnect electrical supply from the water heate r. 2. Shut off the water supply to the water heater usi ng (installer supplied) shutoff valve. 3. Open hot water taps to drain and relieve pressure from the plumbing system. 4. Drain water from the units heat exchanger by disconnecting inlet and outlet water connections from the heater. 5. Connect a line (A) from the outlet of the circula ting pump (installer supplied) to the inlet water fittin g on the water heater (see Fig. 65.) 6. Using another line (B), connect the water outlet fitting on the water heater. Route the other end of this line into a descaling reservoir. 7. Using a 3rd line (C) from the descaling reservoir , connect to the inlet side of circulating pump. Inst all a filter on the end of the line in the descaling rese rvoir. 8. Make sure all connections are water tight.. 9. Fill tank with descaling solution so both lines i nside are submersed. We recommend a straight white vinegar solution. If using a commercial descalant, refer to manufacturers instructions for proper dilution ratio. 10.Operate the circulating pump. 11.Make sure there are no leaks and the solution is flowing from the descaling reservoir through the heater and returning to the reservoir. 12.Run solution through the heater until the soluti on returning to the descaling reservoir comes out clea r. (Changing to a fresh solution may be necessary during this process). 13.Disconnect all lines and drain all solution from heat exchanger. Properly discard of solution. 14.Position a container below the hot water outlet and connect cold water supply. Open cold water supply shutoff valve and flush heat exchanger with clean water. 15.Shut cold water shutoff valve and reconnect hot water supply to the water heater. 16. Reconnect electrical supply to unit, open water shutoff valves, and return the unit to service. Fig. 65 6.4 Condensing heat exchanger unit The condensing heat exchanger unit must be checked once a year by a qualified and trained technician. If repairs are needed, the repairs should be done by a cer- tified Bosch technician. Fig. 66 Condensing heat exchanger unit Condensing heat exchanger unit maintenance ; B Shut off power. Disconnect power cord. B Dismantle all inlet, outlet pipes and the condensat e tube from the condensing heat exchanger unit.
6 720 644 894 Maintenance and service43 B Remove the condensing heat exchanger unit from the appliance by pulling it towards you. B Dismantle all parts for inspection and cleaning. Fig. 67 Condensing heat exchanger B Check the condensing heat exchanger for any obstruction. B Flush the condensing heat exchanger unit with water . B Check all gasket and o-rings for damage and replace if necessary. B Assemble the condensate unit and all other parts in reverse order of disassembly. 6.5 Adjusting CO2 The CO2 can only be adjusted by a certified gas technician with a calibrated CO 2 analyzer. Static Gas Pressure: “ WC P1 Operating Pressure: “ WC The P1 minimum operating gas pressure is 3.5 WC fo r Natural Gas and 8 WC for Propane. Do not proceed i n adjusting CO 2 until pressure is at or above these levels, but not to exceed 10.5 WC for Natural Gas and 13 WC for Propane. A. Once Gas Pressure is adequate B Press ON/OFF button to turn OFF the heater. B Remove brass flat head screw on the exhaust collar as seen in Fig. 68. B Insert CO 2 analyzer probe into the measuring port. The tip of the probe should be in the center of the flue pipe (approx 1.5 inserted). Avoid air gaps between probe and measuring port as they can alter readings . Fig. 68 Measuring port B While holding the Program (P) button, press the ON/ OFF button to turn ON the heater (see Fig. 69). As soon as ‘188’ flashes on the display, release the Program button. The display should now read P2. Press button until “P1” appears on display. Fig. 69 B. Measuring CO 2 (Combustion cover Installed): B Open all hot water taps to achieve a flow rate of a t least 6 gallons per minute. (1 tub and 2 sinks shou ld be sufficient). If heater display reverts back to P 2, open more hot water fixtures to allow sufficient fl ow. Press + until P1 reappears on the display. B Record the CO 2 reading in P1 below. (Analyzer reading may take several minutes to stabilize). B Press the ‘+’ button until P2 appears. Unit will ra mp down to low fire and the water flow should decrease . B Record the CO 2 reading in P2 below. P1 CO 2 Reading: % CO2 P2 CO2 Reading: % CO2 i It is important to inspect and propely replace the gaskets and o-rings. i CO2 adjustment is required in Natural Gas installations where energy content is less than 900 BTU/cuft, and in installations with repeated unresolved EA and EC errors (ref. to page 49 “Problem solving”). Caution: One factor that may affect CO 2 levels is improper gas pressure. Please see Chapter 3.14 for the procedure to measure gas pressure and record your findings below:
6 720 644 89444 Maintenance and service Note: When making adjustments, make sure combustion cover is installed. C. Adjusting CO 2: Note: P1 adjustment will change the P2 reading. Confirm the P1 value BEFORE adjusting the P2 level. 1. If P1 CO 2 level is off: B Loosen yellow painted Phillips screw (1) and cover should rotate down (2) revealing a recessed brass slotted screw. Fig. 70. B Turning the slotted screw counter clockwise will raise P1 CO 2 levels and clockwise will lower P1 CO 2 levels. Adjustments to the slotted screw will also change P2 CO 2 levels. B After bringing the P1 CO 2 readings in proper range, press the button to enter the P2 mode. Verify CO 2 readings in P2 mode. 2. If P2 CO 2 level is off: B Remove yellow painted #40 Torx cover from the front of the gas valve. (Fig. 71) A plastic #40 Torx screw will be revealed. B Turning the plastic #40 Torx screw counter clockwise will lower P2 CO 2 levels and clockwise will raise P2 CO 2 levels. Note : This screw adjustment is very sensitive and should be made in small increments. It may take se veral minutes for readings to stabilize. 3. Verify both P1 and P2 CO 2 readings are within the ranges specified in table 24. Repeat steps 1 and 2 as necesssary until CO 2 values are within the specified ranges. Final Readings P1 CO 2 Reading: % CO2 P2 CO2 Reading: % CO2 D. Returning to Service: 1. Return slotted screw cover to original position. 2. Reinstall Torx cover. 3. Remove CO 2 analyzer probe and reinstall flathead screw with gasket in exhaust collar. 4. Press ON/OFF button to turn OFF the heater and then turn ON the heater. 5. Heater is ready for normal operation. Fig. 70 Adjusting P1 CO 2 level Fig. 71 Adjusting P2 CO 2 level CO2 range (%) Max. CO level (measured) Nat. Gas max. inputP1 7.8 % - 8.4 % < 250 ppm min. inputP2 1.5 % - 1.8 % < 60 ppm LP Gas max. inputP1 9.5 % - 10.1 % < 250 ppm min. inputP2 1.9 % - 2.2 % < 60 ppm * Values above are for climate controlled condition s. Inputs such as gas pressure, heating value of the g as, humidity and temperature of combustion air all impa ct CO and CO 2 values. Changes in these inputs can result in different CO and CO 2 values on the same appliance. Table 24 CO2 & CO target numbers 6720608158-38.1AL
6 720 644 894 Maintenance and service45 6.6 Program values This section describes details on programming the appliance. For most applications the factory defaul t val- ues will provide robust and stable operation. Only adjust the factory settings if the installation req uires changes as indicated in the appropriate section of this manual. Refer to 6.7 Control board diagnostics (page 35) regarding how to access these P-modes. Caution: Misadjusted program values can lead to appliance malfunction, errors, and service calls. ProgramDescriptionFactory DefaultMINMAXComment P1 Maximum Power NG: 51, LP: 5121 NG: 53, LP: 53 see chapter 3.14, page 35 note: reducing P1 values below maximum will reduce maximum power of the appliance. P2 Minimum Power 13 12 20 see chapter 3.3.7, page 20 P3 Remote Controls installed _0 _0 6 see chapter 5.5, page 39 P4 Access to Diagnostic Mode E 0d 10f see chapter 6.7, page 46 P5 Cascade Mode NO NO CC contact Bosch for details P6 Temperature Unit °F °F °C P7 Appliance Type Cd Cd NO Condensing / Non-condensing note: incorrect setting will cause errors. P8 Back light dE dE ON dE turns back light off after 60 seconds from last button pushed, ON turns backlight on permanently P9 Fan Purge runs secondary fan and primary fan when P9 is selected by depressing the “P” - button PH Cascading type IC IC SC This menu is only available w hen cascade mode is selected CC. Contact Bosch Water Heating for details. PC Master/Slave mode CS CS CM Table 25 Program values, factory default settings an d ranges.
6 720 644 89446 Maintenance and service 6.7 Control board diagnostics 1. Press ON/OFF button to turn off the appliance. 2. Press and hold Program button and press ON/OFF button to turn appliance ON. 3. Release the button when 188 appears on the display. The display should read P2 when the program button is released. If not, repeat process. 4. Press and release the button on the control panel until the display reads P4. You are now in the diagnostic mode of the control board. 5. When the display reads P4, press and release th e button once again and the display should read E. 6. Use the and button on the control board to cycle through different diagnostic modes available. 7. Once in the selected diagnostic mode of your choice, press and release the button to display the diagnostic information. EXAMPLE: to read the flow rate in gallons per minut e while the unit is flowing water, cycle to the 3d mode and press the button. A reading of 25 on the dis- play would indicate the heater is reading a flow ra te of 2.5 gallons/minute. 8. Once the information is obtained, press the but- ton again to return to the diagnostic mode menu and scroll to addition diagnostic information. 9. Press ON/OFF button to turn OFF the appliance and back ON again to return heater to normal function. 6.7.1 Working hours To see how many hours the appliance has worked, please enter the “Diagnostic menu” (chapter 6.7); B Select the sub-mode “H0”. Write the number that shows in the display. B Select the sub-mode “H1”. Write the number that shows in the display. B Select the sub-mode “H2”. Write the number that shows in the display. After checking the sub-modes H0, H1 and H2, intro- duce the values in the table below; Example: Calculation of number of working hours, Diagnostic menu E Entry/Exit into sub-modes 0dSet-point temperature 1dInlet water temperature ( °F) 2dOutlet water temperature ( °F) 3d Water flow (gallons/min) 4dGas type (LP or NG) 5dFan speed (Hz) 6dBurner power (%) 7dMaximum power (kW) 8dBack flow temperature ( °C) 9dExhaust temperature ( °C) 1FMost recent error/failure 2F2nd most recent error 3F3rd most recent error 4F4th most recent error 5F5th most recent error 6F6th most recent error Table 26 7F7th most recent error 8F8th most recent error 9F9th most recent error 10F10th most recent error H0Numbers of hours - mode 0 H1Numbers of hours - mode 1 H2Numbers of hours - mode 2 Working hours Number in H0 _____________ + Number in H1 ______ (X 100) =_______ + Number in H2 ______ (X 10 000) =_______ + (H0 + H1 + H2) = Total of hours_________ Table 27 Working hours Number in H0 6060 + Number in H1 5 (X 100) = 500 + Number in H2 0 (X 10 000) = 0 + (H0 + H1 + H2) = Total of hours 560 Table 28 Table 26
6 720 644 894 Troubleshooting47 7 Troubleshooting 7.1 Introduction Many of the questions customers ask regarding opera tion of this unit can be answered by following the troubleshooting steps as outlined below. Visit our web site at www.boschpro.com for more detailed troubleshooti ng. For best results, perform each step before proceedi ng to the next. The suggested solutions may require that the cover be taken off. (See Page 7. Fig. 3). 7.2 Burner does not ignite when hot water is turned ON It is recommended to use “Control board diagnostics ” page 46, chapter 6.7 as a tool for problem solving. 1. If the display is blank, verify power to outlet. (120VAC/ 60Hz properly grounded circuit required). Verify th at the heater power button is pressed ON. 2. Verify the fuses in the control board are good. T o access fuses, the control board must be removed. S ee chapter 4.2, page 36. 3. Make sure cold water inlet connection is plumbed to the right side of heater when facing unit. See Fig. 32, page 29 . 4. A minimum of 0.5 gallons per minute (GPM) (1,9 l/m) is required to activate the heater. A quart container s hould fill in 23 seconds or less, from hot water tap only , to activate heater. 5. Clean inlet filter screen per chapter 3.9, page 29. 6. Inspect the water path for obstructions. Make sur e all showerheads, faucet aerators and whole house filter s are clear of debris. 7. The heater activates when the water flow through the unit is at or above the required minimum of 0.5 GPM (1,9 l/m). A crossover in the hot and cold plumbing pipes creates back pressure on the water flowing through the heater. Therefore, a higher flow rate t han normal is needed to force the heater to activate. T o check for a plumbing crossover, shut off the cold w ater supply to the water heater. Then open all of the ho t water taps served by the heater. Wait 10 minutes an d check for water flow at each tap. There should be n o water flowing. Any continuous flow of water, small or large, indicates a crossover is present and must be corrected. Consult a professional plumber for help in correcting a crossover. Failing single lever faucet mixing valves are common causes of plumbing crossovers. 8. With the power button pressed switch turned to OF F and the power supply cord unplugged, remove the units front cover (See Page 7. Fig 3). Check wire connections between the water valve, control unit a nd electrode set. See chapter 12.2, page 59 for location of these parts. 9.Water heater in solar mode. If inlet water temperat ures exceed the water heaters set temperature, the burn ers will not ignite and the solar mode indicator will s how on the display. See Fig. 54, page 37. 7.3 Water is too hot 1.Selected temperature on the unit is too high. To lo wer output temperature, see chapter 5.4, page 38. 2. Clean inlet filter screen per chapter 6.1, page 41 to increase flow through the heater. 3. Inspect the water path for obstructions. Make sur e all showerheads, faucet aerators and whole house filter s are clear of debris. 4. Confirm the heaters gas type coincides with the type of gas being supplied. See Fig. 2, page 6 for location of rating plate. 5. Avoid restrictive outlets. Clean all showerheads a nd faucet aerators. It may be necessary to upgrade to higher flow rate shower heads if allowable by local code. 6. In areas where the water has a high mineral conte nt, periodic descaling may necessary. See chapter 6.3, page 42 for directions. 7.Ensure the temperature sensor is making contact and firmly mounted on the hot water pipe. 7.4 Water is not hot enough 1.Selected temperature on the unit is too low. To rai se output temperature, see chapter 5.4, page 38. 2. Clean inlet filter screen. See chapter 6.1, page 41 to increase flow through the heater. 3. Inspect the water path for obstructions. Make sur e all showerheads, faucet aerators and whole house filter s are clear of debris. 4. Confirm the heaters gas type coincides with the type of gas being supplied. See Fig. 2, page 6 for location of rating plate. 5. Check inlet gas particle screen for blockage at g as inlet connection on bottom of unit. 6. Verify gas pressure is in accordance with specifi cations in chapter 3.14, page 35. A gas pressure reading is needed to proceed further. Contact your original installer or a local certified gas technician to ob tain this reading. 7. Cold water is mixing into the hot water lines (pl umbing crossover). A plumbing crossover can unintentionally mix cold water with the hot water leaving the heate r. The end result is a cooler water temperature than desir ed. To check for a plumbing crossover, shut off the col d water supply to the water heater. Then open all of the hot water taps served by the heater. Wait 10 minute s Warning: If you are unable to perform the tasks listed below, or need additional assistance please contact your original installer or a licensed gas technician.
6 720 644 89448 Troubleshooting and check all taps for water flow. There should be no water flowing. Any continuous flow of water, small or large, indicates a crossover and must be corrected. Consult a professional plumber for help in correcti ng a crossover. Failing single lever faucet mixing valve s are common causes of plumbing crossovers. 8.Ensure the temperature sensor is making contact and firmly mounted on the hot water pipe. 7.5 Low water flow/pressure 1.Too many hot water applications are being used simultaneously or too much flow is demanded. The water heater will effectively support two 2.0-2.5 G PM shower heads simultaneously or multiple sink applications. Greater draws will result in a water pressure drop and reduced flow at taps. 2. Ensure that gas pressure is in accordance with specifications in chapter 3.14, page 35. A gas pressure reading is needed to proceed further. Cont act your original installer or a local certified gas te chnician to obtain this reading. If gas pressure is inadequa te, the water heater will close its motorized water valve, reducing the hot water flow rate in an attempt to r each the selected output temperature. 3. If selected temperature on the unit is set too hi gh for the demanded flow rate, the water heater will close its motorized water valve, reducing the hot water flow rate in an attempt to reach the selected output temperat ure. Lowering the selected temperature will allow the motorized water valve to open up for increased wate r flow rate. 4. Clean inlet filter screen per chapter 6.1, page 41. 5.Inspect the water path for obstructions. Make sure all showerheads, faucet aerators and whole house filter s are clear of debris. 7.6 Hot water temperature fluctuates at tap 1.Hot water is very hot out of the water heater, requ iring mixing in cold water in order to attain a useable h ot water temperature. The addition of too much cold wi ll overpower hot water flow from the tankless water heater. If this slows the flow through the tankless water h eater below its activation point, it will shut off the bu rners. The end result is nothing but cold water coming out of the outlet. Consult www.boschpro.com for a detailed service bulletin on overcoming temperature fluctuat ions. 2. Unbalanced pressure in water lines. Any restrictio n in the water heater, such as a clogged inlet filter sc reen, can result in unequal pressures between the cold an d hot water lines. In such cases, when mixing in the higher pressure cold water at the tap, the lower pressure hot water can be overpowered. This will shut down the burners because the hot water flow rate fell below the minimum flow rate required for activation. Verify i nlet filter screen is clean and clear of debris. See chapter 6.1, page 41 for inlet filter cleaning instructions. 3. Heater deactivated by temperature balancing valve s. If the outlet water temperature is set too high, the h eater can produce temperatures that are too hot. A temperature balance shower valve will automatically mix in cold water to reduce the hot water temperature. In the event of any temperature instability at a fixture u sing a temperature balancing valve, refer to the valve manufacturer for instructions on internal adjustmen t setting. An adjustment should be made to minimize th e amount of cold water the valve is adding. Additional ly, the temperature setting on the heater can be lowere d to prevent the temperature balance valve from mixing i n too much cold. 4.Inlet water pressure is erratic due to fluctuating supply water pressure. For installation on a private well system with the use of a pressure tank, the lowest pressur e range setting recommended is 40 - 60 psi (2.75 - 4. 15 bar). Consult your installer or local plumber for effective ways to maintain constant water pressure to the appliance when on a well system. 7.7 Noisy burner/heater during operation 1.Sealed combustion leak. Make sure combustion cover is securely fastened. Ensure the exhaust vent adapt or is properly sealed with supplied gasket. Leaky seals create improper combustion resulting in noise. 2. Improper venting. Venting that is unsealed, the w rong material, too big in diameter or too long in run wi ll result in unstable burner flames and noise. Ensure venting is in accordance with specifications in chapter 3.3, page 10 . 3. Lack of adequate combustion air. Drawing combusti on air from a room area of inadequate size will result in unstable burner flames and noise. Improper piping o f combustion air to the outside or insufficient space will result in unstable burner flames and noise. Ensure adequate combustion air is provided from the unit i n accordance with specifications in Section 3.4, page 24 Combustion Air Requirements. 4. Cross contamination. Ensure that intake and exhau st terminations maintain required clearances as stated in chapter 3.3, page 10. Cross contamination between intake and exhaust may cause unstable burner flames and noise. 5. Lack of gas pressure. Inadequate gas pressure wil l cause the fuel-to-air mixture (CO 2) to be out of adjustment. This will result in unstable burner fla mes and noise. Ensure gas pressure is in accordance wit h specifications in Section 3.14, page 35 Measuring Gas Pressure. A gas pressure reading is needed to proceed further. Contact your original installer or a local certified gas technician to obtain this reading. 6.Verify proper CO2 readings per chapter6.5, page 43. CO 2 adjustments must be done by a certified gas technician with a calibrated combustion gas analyze r.
6 720 644 894 Problem solving49 8 Problem solving 8.1 Error code diagnostics i To remove error code from the display, press the reset button. DisplayCauseSolution Fault in the flue gas limiter. Temperature above 230 °F (110 °C) inside the cabinet. 1. Check continuity of the flue gas limiter (see Fig. 77, page 57). Go to steps two and three to determine flue gas lim iter fault and repair it. 2. Check for flue gas leakage around the top and bo ttom seals of heat exchanger, use mirror to check around the rear as well as the viewing window. 3. Check that flue gas limiter connector and spade connections are secure. 4. Unplug heater and check the wiring harness conne ctions on the control board. Exhaust temperature sensor - happens if sensor is disconnected or in short circuit or appliance selection on “P7” mode is not correct. 1. Check exhaust temperature sensor connection. See Fig. 77, #1, page 57. 2. Check sensor (ref. page 54, chapter 10). 3. Check “P7” mode: the water heater requires setting “Cd” for condensing appliances . Backflow temperature sensor defect - happens if sensor is disconnected or short circuit. 1. Check backflow temperature sensor connection. See Fig. 77, #1, page 57. 2. Replace exhaust temperature sensor. 3. Check sensor (ref. page 54, chapter 10). Outlet temperature sensor fault (Temperature below 36°F or above 210°F). 1. Check red wire connections at hot water temperat ure sensor. Clean terminals with an eraser. If badly corroded, replace sensor and wire harness. See Fig. 72, page 53. 2. Sensor may trip if water temperature drops below 36°F to protect heater from freezing conditions. Any damage due to freezing conditions is not covered under warranty. 3. In areas where water has a high mineral content, periodic descaling may necessary. 4. Check sensor (ref. page 54, chapter 10). (Flashing) Outlet temperature sensor not sensing expected output temperature. (Status message, not an error). 1. Check that the sensor is firmly attached to the vertical section of the hot water pipe, see Fig. 83, page 64. 2. Ensure that hot water sensor is not placed on an y bends in the hot water pipe or misreading may occur. 3. Check gas pressure. Low gas pressure may prevent the heater from reaching desired output temperature. 4. Check supply voltage. It must be 120VAC and prop erly grounded. 5. Possible defective control unit call Bosch Water Heating for further instructions. Table 29 * By installer or service technician only.
6 720 644 89450 Problem solving Primary fan rotation too low in operation. 1. Disconnect power supply cord and check wire conn ection on back side of fan and the connectors on the control board, see Fig. 84 , page 65. 2. Check supply voltage. It must be 120VAC and prop erly grounded. 3. Check venting specifications are met. Long vent lengths, venting with more than three elbows, blocked vent o r combination venting may cause this failure. 4. Ensure intake and exhaust terminations maintain the required clearances stated in the manual. Cross contaminatio n between intake and exhaust may cause the fan to alter its r otational speed. 5. Check gas pressure. Low gas pressure may cause t he fan to change its speed to meet desired temperature. 6. Possible defective control unit call Bosch Water Heating for further instructions. No rotational speed sensor signal from primary fan. 1. Disconnect power supply cord and check wire conn ections on back side of fan and the two connectors on the cont rol board, see Fig. 84, page 65. 2. Check supply voltage. It must be 120VAC and prop erly grounded. 3. Possible defective component in fan or defective control unit call Bosch Water Heating for further instructions. (Flashing) Water flow signal over specified maximum value. Water flow > 10 gallon/min. (Status message). 1. Disconnect power supply cord and check wire conn ections on water valve and the two connectors on the control b oard, see Fig. 84 , page 65. 2. Excessive water pressure and flow. Ensure water pressure is less than 150psi and flow rate is below 10 gallons per minute. Over-temperature detected by outlet temperature sensor. Temperature > 185 °F 1. Check that the sensor is firmly attached to the horizontal section of the hot water pipe, see Fig. 83, page 64. 2. Check red wire connections at hot water temperat ure sensor. Clean terminals with an eraser. If badly corroded, replace sensor and wire harness. 3. In areas where water has a high mineral content, periodic descaling may be necessary. See chapter 6.3, page 42 for directions. 4. Check sensor (ref. page 53, chapter 9). Cold water temperature sensor fault. 1. Check connector on wires coming from top of wate rvalve for a secure connection. See Fig. 77, page 57. 2. Sensor may trip if water temperature drops below 36°F (2 °C). Protect heater from freezing conditions as any dama ge due to freezing conditions is not covered under warranty. 3. Check sensor (ref. page 54, chapter 10). DisplayCauseSolution Table 29 * By installer or service technician only.