Troubleshooting Guide Condensing Models On‐Demand Water Heater Troubleshooting Guide Direct Vent Indoor models (520 Indoor (T‐H2‐DV), 320 Indoor (T‐H2S‐DV)) Outdoor models (520 Outdoor (T‐H2‐DV), 320 Outdoor (T‐H2S‐DV)) 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……………………………………………………….……….
Troubleshooting Guide Table 1: SPECIFICATIONS ‐ 520 (T‐H2) / 320 (T‐H2S) Direct Vent Indoor* and Outdoor 520 Direct Vent Indoor (T‐H2‐DV) Model 520 Outdoor (T‐H2‐OS) Dimensions Combustion Water control 73 lbs. Max Operation 73 lbs. 199,000 Installation 13,000 Power vent Direct‐vent Outdoor Fan motor Max Min 71 lbs. 180,000 Min Direct‐vent Outdoor PWM turbo fan LP 4.9” WC Natural 3.6” WC LP 1.0” WC Natural 0.7” WC LP 4.3” WC Natural 2.5” WC LP 1.0” WC Natural 0.7” WC LP 4.6” WC Natural 2.
Troubleshooting Guide 2. INTRODUCTION This manual provides the necessary information for troubleshooting the 520 (T‐H2) and 320 (T‐H2S) tankless water heaters. This manual 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 520 (T‐H2) and 320 (T‐H2S) Installation Manual as the primary source of information. Refer to it along side this manual throughout the troubleshooting process.
Troubleshooting Guide 3. NORMAL OPERATION Becoming familiar with how a tankless water heater normally operates may help to troubleshoot it. Assuming it is properly installed with appropriate gas, water, and electric connections, the following is how it should operate: 1) ACTIVATION a. A hot water tap is opened enough that the flow sensor detects a flow rate through the heater greater than the activation point of 0.5 gpm. b. The fan activates after flow is detected. c.
Troubleshooting Guide 4. INSTALLATION These guidelines are quick overviews on the main points of installation – For all installation details, refer to the 520 (T‐H2) or 320 (T‐H2S) Installation Manual that is packaged with every heater. Follow all codes pertaining to the installation of a gas appliance. VENTING OUTDOOR MODEL INSTALLATION: • • Outdoor installations fall under the Direct Vent Clearances published by ANSI Z223.1/NFPA 54 or CAN/CSA‐B149.
Troubleshooting Guide GAS LINE • • • Incorrect gas type, NG (Natural) or LP (Propane), is one of the most common and simple problems. Verify the correct gas type by: o Checking that the stamp on the burner manifold matches the gas type supplied at the application site. o Checking the box that the unit comes in for the gas type. o Minimum gas line size for the tankless water heater is ¾ inch pipe. The size can be greater depending on the distance to the gas meter or regulator.
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. This can be verified by observing the computer board 3‐digit LED display. If it is not lit, the computer board is not being powered.
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 • • The flow adjustment valve could be obstructed due to hard water scale or debris, causing lower than expected water flow. Verify water flow with a graduated container or with the remote temperature controller, if one is installed. The output thermistor could be compromised. This component may be checked by entering the Diagnostics Mode on a remote controller, if one is installed.
Troubleshooting Guide UNIT DOES NOT IGNITE WHEN WATER GOES THROUGH IT • • • • • • • • • Is the flow rate over 0.5 gpm? See if the unit initiates when you increase demand of water being drawn through the unit (e.g. opening up more hot fixtures). Check that the gas line is open and is purged of air (p. 24). Check that the filter on the cold water inlet is clean (p. 23). Check for reverse connection and cross connection (p. 24).
Troubleshooting Guide UNIT HAS POWER, GAS, AND WATER BUT DOES NOT TURN ON • • • For new unit installs, check to make sure the unit is not plumbed in backwards. o Shut off cold water feed only. o Open nearest hot water tap. Water flow should stop. If not there is a cold water cross connection. o Open Pressure Relief Valve. Water flow should stop. If not unit is plumbed in backwards. Clean the filter (p. 23). If the fan never initiates, check for a fouled water flow sensor (p. 34).
Troubleshooting Guide 5.3 TROUBLESHOOTING ‐ ERROR CODES • • All 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 TM‐RE30 Remote Controller (if installed) or on the 3‐digit 7‐Seg LED at the center of the computer board to communicate the source of the problem. Consult the following chart for the cause of each error code.
Troubleshooting Guide Example: If Unit #2 has the “321” error code (inlet thermistor failure) • • Water heater #2: It will display “321” on the 7‐Seg LED, just like in the Single Unit example. TM‐RE30: It will display “232” on its screen. The first “2” indicates that Unit #2 has the error. The “32” indicates the first two digits of the “321” error code.
Troubleshooting Guide ERROR CODE 111: IGNITION FAILURE Heater does not fire after three failed attempts at ignition. 1) Verify that the hi‐limit switch is not tripped. Turn the power off to the unit. Push the white button in. The switch will reset when you hear and feel the button click. Turn the power back on and test the heater. If the unit fires on, the cause of the hi‐limit trip must be determined. Please contact the technical service department for further technical support. 2) Check the gas supply.
Troubleshooting Guide 2) Check the gas supply. Verify that sufficient gas is being supplied to the heater and the gas line is cleared of debris. a. It is possible there is a faulty pressure regulator at the gas meter. b. For propane units, colder periods of the day result in a cold regulator and may cause this problem. 3) Verify that the gas supply pressure is within specifications when the heater is in standby and when the heater is running.
Troubleshooting Guide 4) If the error code persists, replace the thermistor. ERROR CODE 331: MIXING THERMISTOR 1) Check that the wire connections are secure and free of burns or cuts. The mixing thermistor is embedded in the water outlet connection. 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. 23. b. Remove the computer board to access the mixing thermistor.
Troubleshooting Guide ERROR CODE 441: FLOW SENSOR Part of an Easy‐Link 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. 2) Verify that the wires are connected to the computer board. 3) Check the inlet filter for any debris. See p. 23. 4) Check the flow sensor for debris. ERROR CODE 510: ABNORMAL MAIN AND/OR SOLENOID GAS VALVE Driving circuit fault for the main or solenoid gas valves.
Troubleshooting Guide b. Move the computer board out of the way. This involves three screws and removing any restricting wires connected to the PCB. c. Locate the two Phillips head screws fitted at the top of the fan motor to the combustion chamber box. Two holes are located directly at the bottom of the casing that line up with the two screws. Using an 8” screwdriver, remove the screws. d. Slide the fan out towards the left. e.
Troubleshooting Guide e. Test the heater. 6) The water control valve may need to be replaced if the valve cannot be cleaned. Contact the technical service department. ERROR CODE 661: ABNORMAL WATER BYPASS 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.
Troubleshooting Guide ERROR CODE 721: FALSE FLAME DETECTION 1) First and foremost, shut off all gas and power to the unit. The problem could be the flame sensor, but if it isn’t, this is a very dangerous situation. 2) Contact the technical service department for further assistance. ERROR CODE 741: MAIN REMOTE CONTROL PROBLEM This error code only occurs when there is a miscommunication between the temperature remote controller and water heater.
Troubleshooting Guide 5.4 TROUBLESHOOTING – PROCEDURES Verifying proper Dipswitch settings p.22 Draining the unit p.23 Cleaning the filter p.23 Checking for a Cross Connection p.24 Check for Reverse Connection p.24 Check gas supply pressure p.24 Purge the gas line of air p.24 Adjusting manifold pressure p.25 Resetting the Computer Board p.26 Checking the OHCF p.26 VERIFYING PROPER DIPSWITCH SETTINGS: • Incorrect Dipswitch settings can cause a 031 error code.
Troubleshooting Guide Table 5 – Right Bank of Dipswitches No.
Troubleshooting Guide 3) Securely screw the filter back into place. Hand‐tighten only. CHECKING FOR A CROSS CONNECTION: 1) 2) Turn off cold water supply. Turn on all hot water fixtures. a. The water should eventually completely drain. b. If water continues to run, the fixtures and plumbing system needs to be checked. c. Cold water cross connections may be related to a recirculation pump application, a bad check valve, or missing check valve in the application.
Troubleshooting Guide CHECKING MANIFOLD GAS PRESSURE: 1) Ensure that the unit is not in operation. 2) Remove the screw off the manifold port. 3) Connect a manometer to the manifold port using a tube (Figure 1). Ensure that this connection is secure enough to prevent gas leak. 4) Run water to activate its operation. It is suggested that a large amount of flow is drawn in order to prevent Figure 26 overheating during max burn.
Troubleshooting Guide RESETTING THE COMPUTER BOARD: 1) Verify that there is no water flowing through the unit. 2) If a temperature remote controller has been installed, turn the power off to the remote. 3) Turn off power to the unit, and then turn on again. 4) Push and hold the “INC” and “DEC” buttons on the computer board simultaneously for several seconds until the red LED lights up solid. See Figure 5.26. 5) Use the Power ON‐OFF switch to turn the unit off “Increase” button then on again.
Troubleshooting Guide 6. MAINTENANCE Become familiar with the components before attempting these procedures, utilizing the Installation Manual and referencing the component schematic on the last few pages of the manual. Safety is the most important part of this guide. These procedures must be done by a licensed competent technician. A.O. 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.
Troubleshooting Guide CLEANING THE COMBUSTION COMPONENTS Procedure for cleaning the fan, burner, Flame Sensor and AFR, as used by all Service agents. 1) TOOLS ‐ Gather the following materials together: a. 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 ‐ Disconnect power to your unit by either unplugging it from the wall outlet, or by the circuit breaker, depending on the setup.
Troubleshooting Guide 7) 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. Refer to Figure 6.4 for the location of these screws. b. Remove the burner. It may be hard to take out, so try the following: i.
Troubleshooting Guide 10) COMBUSTION CHAMBER ‐ Inspect the combustion chamber with a bright flashlight. a. Remove the exhaust venting from top of the unit for the DV model b. Place one towel at the bottom of the combustion chamber, protecting the discharge of the fan (fan port), as well as drape another towel covering the square opening of the combustion chamber (to prevent airborne debris) c. Turn on the shop vacuum and vacuum all of the dirt from the combustion chamber. d.
Troubleshooting Guide REPLACING THE HEAT EXCHANGER 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. Lime scale will form on the inside of the heat exchanger tubes readily at high temperatures.
Troubleshooting Guide 6) SECONDARY HEAT EXCHANGER a. Disconnect the top of the condensate P‐loop hose. Pinch the clamp to remove the hose. b. Remove the two clips from either side of the plastic secondary heat exchanger manifold pipes. c. Remove the seven screws around the perimeter of the heat exchanger, and then slide it out. 7) WATERWAYS a. Disconnect the small drain clip on the left. b. Remove the two clips below the water control valve. Figure 36 Figure 35 Figure 37 8) REMOVE THE HEAT EXCHANGER a.
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. Install the following items from the old exchanger onto the new one: i. Water control valve ii. Overheat Cutoff Fuse iii. Freeze protection blocks iv. Plastic pressure port v. Hi‐Limit switch vi. Hot water thermistor 10) REASSEMBLE ‐ Reassemble the unit in reverse order. Key points to remember: a.
Troubleshooting Guide CHECKING THE FLOW SENSOR If the tankless unit is properly connected to water, gas, and power supplies but the fan motor does not initiate when water is run through it, the flow sensor is most likely not working properly and not telling the PC Board to initiate. 1) TOOLS ‐ Gather the following materials together: a. Degreaser in a pump action bottle b. #2 Philips Screw Driver c. Flashlight 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.
