Troubleshooting Guide 910 / 910 ASME (T‐M50 / T‐M50 ASME) On‐Demand Water Heater Troubleshooting Guide 910 / 910 ASME (T‐M50 / T‐M50 ASME) A.O.
Troubleshooting Guide Table of Contents Troubleshooting Guide 1. SPECIFICATIONS.……………………………………………………………………………..……………………3 2. INTRODUCTION.…………………………………………………………………………………..………………4 3. NORMAL OPERATION…………….………………………………………………………………………..…..5 Activation………………………………………………………………………………………………….5 Operation.………………………………………………………………………………………………..5 Shutdown……….………….………………………………………………………………………..…..5 4. INSTALLATION….…………………………………………………………………………….…………………….6 Venting…………….………………………………………………………………………………..…..…6 Gas Line…………….
Troubleshooting Guide 1. Table 1 ‐ SPECIFICATIONS Unit Model 910 / 910 ASME (T‐M50 / T‐M50 ASME) Unit dimensions H25.3"×W24.8"×D11.8" Weight 102 lbs. Combustion INPUT BTU/h Water control Operation 380,000 Min 15,000 Combustion System Power vent Installation Indoor, Outdoor, Direct vent Fan motor PWM Turbo fan Manifold Pressure* Features Max LP 3.7” WC Natural 2.7”WC LP 0.9” WC Natural 0.7” WC Max Min Flow rate 0.5 to 14.5 GPM Available set temp.
Troubleshooting Guide 2. INTRODUCTION This manual provides the necessary information for troubleshooting the 910 / 910 ASME (T‐M50 / T‐ M50 ASME) tankless water heaters. It will be effective in helping your troubleshooting needs as long as the instructions are followed in the intended order. Here is how to use this manual: • First refer to the Installation Manual as the primary source of information. Refer to it along side this manual throughout the troubleshooting process.
Troubleshooting Guide 3. NORMAL OPERATION The 910 / 910 ASME (T‐M50 / T‐M50 ASME) is a combination of two tankless water heaters in one case, as pictured below. When troubleshooting this unit, it is important to identify which major assembly, left or right, is the side that the problem is located. Once it is determined which side contains the problem, unless specifically stated, the procedures for troubleshooting and maintenance are exactly the same for both the left and right heat exchanger assemblies.
Troubleshooting Guide 4. INSTALLATION 1. Follow all local codes, or in the absence of local codes, follow the most recent edition of the National Fuel Gas Code: ANSI Z223.1/NFPA 54 in the USA or CAN/CSA B149.1 Natural Gas, Propane Installation Code in Canada. 2. All gas water heaters require careful and correct installation to ensure safe and efficient operation. This manual must be followed exactly. Read the “Safety Guidelines” section in the installation manual. 3.
Troubleshooting Guide 5. TROUBLESHOOTING 5.1 PRELIMINARY CHECKLIST Check all of these basic items before proceeding onto any other section: • GAS/WATER/ELECTRIC: o The gas supply valve should be fully open. o Verify the correct gas type is being used, NG or LP. o The water supply valve should be fully open. o The unit should be connected to a 120 VAC 60 Hz power supply. • REMOTE: If you are using a remote controller, the remote’s power button must be turned on.
Troubleshooting Guide 5.2 TROUBLESHOOTING ‐ GENERAL PROBLEMS Proceed to the Error Codes section if an error code is identified. For other common problems that do not involve an error code, see if the following items help: The water is not hot enough. The water is too hot. Temperature fluctuates when a fixture is opened. Unit does not ignite when water goes through it. It takes a long time to get hot water at the fixtures. The fan motor is still spinning after operation has stopped.
Troubleshooting Guide remote. For instructions on how to do this, refer to the Maintenance Sheet, packaged with every tankless water heater and located behind the front panel of the unit. TEMPERATURE FLUCTUATES WHEN A FIXTURE IS OPENED • • • • • • • • Make sure the unit is installed properly using the Proper Installation section (p. 6) of this guide. Check the flow and temperature right at the unit at the pressure relief valve.
Troubleshooting Guide See that a check valve is installed between the pump discharge and the connection to the cold water supply. A malfunctioning or missing check valve will cause cold water to back‐feed into the system. If you use the remote controller, is the remote power button turned on? Check to see if the Computer board is receiving power. This can be verified by observing the computer board red LED. o If it is not lit, the computer board is not being powered.
Troubleshooting Guide EASY‐LINK SYSTEM SETUP (MULTIPLE HEATER SETUP) • • Refer to the Installation Manual for proper setup. Unit Numbering o The master unit will always be assigned number 1. The remaining units will be randomly assigned numbers 2‐4 (if there are 4 units in the Easy‐Link system).
Troubleshooting Guide 5.3 TROUBLESHOOTING ‐ ERROR CODES • • • • All tankless units are self diagnostic for safety and convenience when trouble shooting. If there is a problem with the installation or the unit, it will display a numerical error code on the Remote Controller (if installed), or on the 7‐Seg LED on the computer board to communicate the source of the problem. The 910 (T‐M50) is two units combined into one case.
Troubleshooting Guide ERROR CODE 031: INCORRECT DIPSWITCH SETTINGS 1) Turn off the power supply. 2) Remove front cover and locate the dipswitches on the center of the computer board. 3) Check the dipswitch settings on the left and right banks. Refer to p.20 for the correct dipswitch positions. a. Gas type is a common dipswitch error. b. Most other switches should be on default setting UNLESS the particular setup requires otherwise. c.
Troubleshooting Guide 3) Verify that the gas supply pressure is within specifications when the heater is in standby and when the heater is running. 4) Check that the clear plastic tube connecting the proportional gas valve to the combustion chamber is attached. 5) The overheat cutoff fuse (OHCF) may have been compromised. For procedures on how to check whether the OHCF is intact, refer to p. 25. If the OHCF has been compromised, contact the technical service department for further assistance.
Troubleshooting Guide ERROR CODE 311: OUTPUT THERMISTOR 1) Check that the wire connections are secure and free of burns or cuts. The output thermistor is located on the heat exchanger on the right side. 2) Check the resistance value; it should be about 9.0kΩ at room temperature (about 74°F). 3) Clean the thermistor. a. Drain the unit of water. See p. 22. b. Remove the fastener holding the output thermistor and pull out the sensor probe. Clean the probe to a silver finish.
Troubleshooting Guide ERROR CODE 391: AIR‐FUEL RATIO ROD FAILURE 1) Check that the wire connections are secure and free of burns or cuts. 2) Check that the clear plastic tube connecting the proportional gas valve to the combustion chamber is attached. 3) Clean the AFR (p. 26). ERROR CODE 441: FLOW SENSOR Figure 10 Part of an Easy‐Link or Multi‐Unit system, the master unit signaled for an additional heater to activate and it did not. 1) Verify that water is being supplied to the heater in error.
Troubleshooting Guide ERROR CODE 611: ABNORMAL FAN MOTOR 1) Turn off power supply. 2) Check fan motor wiring for any breakages, burn marks on the PC board, or moisture. If moisture is found, allow connection to completely dry before turning power back on. 3) Check fan housing for water. If found, please dry the fan, then test heater. 4) To remove the fan motor. a. Turn off the power supply. b. Move the computer board out of the way. c.
Troubleshooting Guide ERROR CODE 661: BYPASS VALVE FAULT 1) Turn off power supply. 2) Check that all wire connections are secure and free of burns. The flow adjustment valve is located behind the computer board and attached to the cold water inlet. 3) Check for water leakage from the valve. 4) Do a visual inspection of the PCB. Check for connection/breakage of wires and/or burn marks on the board. PCB may need to be replaced. 5) The bypass valve may need to be cleaned. To remove, follow the steps below: a.
Troubleshooting Guide ERROR CODE 761: COMMUNICATION FAILURE 1) This error code only occurs in a multiple heater setup, where there is a miscommunication between master and slave units for Easy‐Link systems. 2) This error code will only be displayed on the master heater. 3) This error indicates that the master unit has lost communication with the indicated heater. 4) Verify that there is power to the unit that has lost communication. 5) See the Installation Manual for proper communication cable setup.
Troubleshooting Guide 5.4 TROUBLESHOOTING ‐ PROCEDURES Verifying proper Dipswitch settings… p.20 Draining the unit………………………………p.22 Cleaning the filter…………………………….p.22 Checking for a Cross Connection………p.22 Check for Reverse Connection………….p.22 Check gas supply pressure………………. p.23 Purge the gas line of air………………….. p.23 Adjusting manifold pressure…………….p.24 Resetting the computer board………… p.24 Checking the OHCF…………………………. p.
Troubleshooting Guide Figure 19 Figure 18 Table 4 – Dipswitches, Center Board, UPPER No. Function 1 Gas Type 2 N/A 3 N/A 4 Pump Mode 5 6 7 Activation of the Freeze Protection Pump for recirculation systems Number of priority combustion units Table 5.4 – Dipswitches, Center Board, LOWER No.
Troubleshooting Guide 4 Activation of Individual Operation mode 5 Direct vent setting 6 Outdoor setting 7 Activation of checking the recirculation pump Enable (Default) Enable Direct vent mode Enable Outdoor Mode Enable 8 Parent/Child setting on Easy‐Link systems Parent Disable Disable (Default) Disable (Default) Disable (Default) Child (Default) DRAINING THE UNIT: 1) 2) 3) 4) 5) Close the manual gas shut off valve. Turn off power to the unit, and then turn on again.
Troubleshooting Guide CHECK GAS SUPPLY PRESSURE: 1) Close the manual gas inlet shut off valve on the gas supply line. 2) Open a faucet. The unit should turn on and the gas in the pipe line should purge. Leave the faucet on to keep the unit running until it shuts down due to lack of gas, and then shut the faucet off. Ignore any error codes that may occur at this time. 3) Remove the screw for the pressure port located on the gas inlet shown on the right. 4) Connect a manometer to the pressure port.
Troubleshooting Guide ADJUSTING MANIFOLD PRESSURE: The manifold gas pressure of the tankless unit can be adjusted by the following procedure. WARNING Adjusting the manifold pressure can cause unexpected combustion conditions during operation, which can cause a health hazard, damage the tankless unit, and or shorten its lifespan. Therefore, changing the manifold pressure is not recommended unless there are very strong reasons to do so (e.g.
Troubleshooting Guide CHECKING THE OVERHEAT CUTOFF FUSE (OHCF): 1) 2) 3) 4) Locate the white OHCF which wraps around the heat exchanger. Find the white clip at the end of the two blue braided wires coming from the OHCF. Unplug the connection. Test for continuity at the end of the OHCF with an ohmmeter. If there is continuity, the OHCF is still intact. Reconnect the plug. If there is no continuity, the OHCF has been compromised.
Troubleshooting Guide 6. MAINTENANCE Safety is the most important part of this guide. These procedures must be done by a licensed competent technician. AO Smith is not liable for the actions of the technician if he/she fails to adhere to any or all safety procedures, specifically in regards to electrical and gas safety. The 910 / 910 ASME (T‐M50 / T‐M50 ASME) is a combination of two tankless water heaters in one case.
Troubleshooting Guide CLEANING THE COMBUSTION COMPONENTS Procedure for cleaning the fan, burner, Flame Sensor and AFR, as used by all Service Representatives. 1) TOOLS ‐ Gather the following materials together: a. Degreaser in a pump action bottle, Sandpaper, Philips Screw Driver, Needle‐Nosed Pliers, Duct Tape, Flashlight, Air Compressor, Shop Vacuum, 3x Towels 2) POWER/GAS ‐ Disconnect power to your unit by either unplugging it from the wall outlet, or by the circuit breaker, depending on the setup.
Troubleshooting Guide GFI screws (right HX only) Gas inlet screw Figure 28 Figure 29 6) BURNER ASSEMBLY ‐ Now proceed to remove the burner assembly. a. Remove the five wide pan head Philips screws holding the burner to the combustion chamber. There are three at the top of the burner. There are two at the bottom of the burner to the back of the combustion chamber. b. Disconnect the rod assembly: Orange flame sensor, Yellow AFR, Black igniter wire c. Remove the burner.
Troubleshooting Guide 7) CLEAN THE BURNER ‐ Use a safe degreaser. a. Protect the burner gasket from direct water pressure. b. c. d. e. IF the gasket becomes compromised, please contact the technical service department for further assistance. Thoroughly saturate the burner with the cleaning solution from the top, down through the slots, as well as the openings in the front of the burner until the burner is soaking wet. Let the burner sit for 5 minutes. Remove the burner from the solution.
Troubleshooting Guide 11) SENSORS – a. Clean the flame sensor and AFR with sandpaper, thoroughly to a bright finish. It is important to be very gentile with the sensor rods while cleaning them, as they will easily bend out of place. Their original position relative to the burner needs to be unaltered in order to function properly. 12) REASSEMBLE ‐ Reassemble the unit in reverse order. Key points to remember: Figure 33 a. Inspect all of the gaskets. b.
Troubleshooting Guide REPLACING THE HEAT EXCHANGER There are many possible causes of a heat exchanger failure: • • Contaminated air with a high level of dust, lint, sand, grease, aerosols or other contaminants, can become airborne and enter the air intake. The contaminants build up within the fan and burner assembly causing abnormal flame conditions due to lack of combustion air, damaging many components of the unit. Scale can build up from very hard water.
Troubleshooting Guide 5) WIRES ‐ There are several wire clips that need to be removed to free the heat exchanger a. Blue wired clips to the left of the heat exchanger, held by a clip on the copper pipe b. Flame sensor (orange), AFR(yellow), and igniter (black) wires c. Screw holding green ground on the top left of the manifold plate d. Thermistor clip on left of the heat exchanger e. Blue heating block wire on right side Right HX items Left HX items Center PCB screws Figure 36 6) FAN a.
Troubleshooting Guide 7) WATERWAYS a. DRAIN THE UNIT of water. Refer to the Draining the Unit procedure in the troubleshooting procedures section. b. Disconnect the waterway clips pictured at the right. c. Disconnect the water control valve wire clip from the top of the PCB. d. Place a dry towel in the bottom of the unit case when dislodging the pipes from their sockets. Figure 38 Figure 39 8) REMOVE THE HEAT EXCHANGER a. The heat exchanger should be free to be removed.
Troubleshooting Guide 9) REPLACE THE HEAT EXCHANGER COMPONENTS a. Remove and inspect the new heat exchanger making sure it is designed for the correct model and is not damaged at all. b. Place the HX on a surface upside‐down on the vent collar, as shown below. Swap the following items: i. Over heat cutoff fuse (OHCF) ii. Two heating elements iii. High limit switch iv. Thermistor (Do not forget red o‐ring) v. Pressure port (bottom of combustion chamber) vi.
Troubleshooting Guide 10) REASSEMBLE ‐ Reassemble the unit in reverse order. Key points to remember: a. All wires must be reconnected. Keep wires dangling out in front of the unit, never push them toward the back where they are not visible; you will forget about them. b. Inspect all of the gaskets. c. Be aware of the various O‐rings on the gas and water valves, along with the waterway clips. d. Reattach all extra components that the manifold screws secure in their places. e.
Troub bleshooting Guide G CH ECKING THE T FLOW W SENSOR R If the tankkless unit is properly p connected to wateer, gas, and power p suppliees but the fan n motor does not initiate when water is run through it, i the flow seensor is most likely not wo orking properly and not tellling the PC Bo oard to initiate e. 1) TOOLS ‐ Gather the e following materials m togeether: a. Degreaser in a pump action n bottle b. #2 2 Philips Scre ew Driver c. Fllashlight d.
Troubleshooting Guide DESCALING THE UNIT Hard water is a severe problem for the copper coils inside heat exchangers. Heat exchanger failure due to scale buildup from hard water conditions is NOT covered by warranty. It is highly suggested that a scale inhibitor be installed before the cold water inlet after this procedure is done. 1) TOOLS ‐ Gather the following materials together: a. Pump: The pump should provide a minimum of 1GPM through the heater b.
