Troubleshooting Table and Diagnostic Guide for Tankless Water Heater

TROUBLESHOOTING

SYMPTOMS/CODES	PROBABLE CAUSES	CORRECTIVE ACTIONS
No hot water & no power to the heater. POSSIBLE CODES: NONE (LED not on)	- Breaker(s) at main panel or sub-panel - No Voltage - Incorrect wiring	- Check / reset breakers — most models have multiple power circuits (refer to heater specifications). Verify that the breakers marked for the heater are actually the breakers serving the heater. - Check for power at the lugs. Refer to the Component Testing Table for proper voltage measurements at the lugs. - If breakers are on and there is no power at the lugs, It may be possible the electrical wiring is out-of phase to one or more of the incoming power circuits. Turn off all power to the heater and re-wire the circuits until all circuits are measuring 208 to 240 volts across each pair of lugs, L1 & L2. It is recommended that this be done by a licensed contractor.
No Hot Water & Power verified at all incoming circuit lugs. POSSIBLE CODES: NONE (LED not on) LED flashing ALL GREEN THE FOLLOWING RED FLASHING CODES: 122 123 126 127 127&142 142	- Check Self Diagnostic Codes, each listed in theDiagnostic Troubleshooting Code section - Heater undersized for application - Tripped High Limit Switch - No water or low water level in heater - Water Leak - Power outage, voltage spike or surge - Control Data Reading Error	Check the LED on the control board for self diagnostic codes. - If LED is flashing red code(s), refer to how to read the code, refer to Diagnostic Codes for possible causes and corrective action. - If LED is solid red and there are two LED’s, the control board is an older version analog control, made prior to May, 1999. The diagnostic codes do not apply to the analog control. Call Microtherm, Inc. for troubleshooting procedure. - No code: Check water demands, including flow rate and inlet water temperature. Also, check the service voltage. If the service is 208 volts AC, and the heating elements are rated for 240 volts AC, the power rating and the flow rate capability of the heater will be decreased. Refer to the heater’s ratings and flow rate specifications. Note: a 127 code may occur during periods of flow that exceed the heater capacity. If possible, throttle back the flow at the faucet or the shut-off valve. Our heaters should be sized for maximum flow rate(s) and the highest temperature rise (which usually occurs in the winter months). - 122 code: Check for a tripped high temp. limit switch. If tripped, turn off all power to the heater. Reset the switch by pushing in the button on the switch itself. Check the switch and brown wires for continuity. If the switch is open, see High Limit Switch Replacement in the Removal and Repair section. Replace the switch. If the switch is not open, check further for possible temperature sensor or temperature sensor wire problems. After adjusting or replacing the temperature sensor, perform the Matching Procedure. - 123 code: Check that the heater is filled with water and that there is no air trapped inside. Purge the hot water lines if necessary. Check operation of back flow preventer (or check-valve). If the heater is filled and there are no leaks, ground both level detect spades on the board. The 123 code should go away. If so, do not leave the level detect grounded out as it will eliminate this very important safety feature. - 126 code: Check for water leaking at the connections to the inlet and outlet fittings, the level detector screws, the limit switches, the elements and the temperature sensors. With all power off to the heater, tighten or replace according to the specifications found in the Removal and Repairsection of this manual. Refer to Diagnostic Codes for more corrective steps. - 127 & 142 codes: The heater needs to be reset. Turn off all breakers to the heater for approx. 30 seconds. Turn on breakers and check LED status. The LED should flash all green and heater should produce hot water. If both codes remain, refer to temperature sensor and heating element testing. Perform theMatching Procedure. - 142 code: The heater needs to be reset. Turn off all breakers to the heater for approx. 30 seconds. Turn on breakers and check LED status. The LED should flash all green and heater should produce hot water. If the 142 code remains, try re-stetting the breakers again. If 142 code persists, refer to temperature sensor testing in the Component Testing Table. If temperature sensors and wires are good, perform Matching Procedure. If the 142 code does not clear, see control board replacement in Removal and Repair section.
Water Not Hot Enough or Fluctuating Temperatures POSSIBLE CODES: NONE 111 & 118 or 117 112 & 118 or 117 113 & 118 or 117 114 & 118 or 117 115 & 118 or 117 127 127 & 142	- Breaker(s) at main panel or sub-panel - Incorrect wiring - Loose connection - Temperature adjusted too low - Heater undersized for application - Temperature sensor problem or bad temperature sensor wire or wire connection - Bad heating element	- 127 code: Check / reset breakers — most models have multiple power circuits (refer to heater specifications). Verify that the breakers marked for the heater are actually the breakers serving the heater. - 127 code: With breakers on, check for power at the lugs. Refer to the Component Testing Table for proper voltage measurements at the lugs. It is possible the electrical wiring is out-of phase to one or more of the incoming power circuits. Turn off all power to the heater and re-wire the circuits until all circuits are measuring 208 to 240 volts across each pair of lugs, L1 & L2. It is recommended that this be done by a licensed contractor. - 127 code: Turn off all breakers and check lugs and heating elements for loose or disconnected wires. If necessary, tighten or reconnect wires and turn on the breakers. Test water. - No Code: Check the thermostat setting. If adjustable knob is turned all the way to the left, temperature output may be below 95 degrees F. Turn the knob to the right to increase temperature. - No code: Check water demands, including flow rate and inlet water temperature. Also, check the service voltage. If the service is 208 volts AC, and the heating elements are rated for 240 volts AC, the power rating and the flow rate capability of the heater will be decreased. Refer to the heater ratings and flow rate specifications. Note: a 127 code may occur during periods of flow that exceed the heater capacity. - 127 & 142 codes: The following codes are also used by the control to identify the problem temperature sensor, (refer to the Diagnostic Codes for more detail): - 111, 112, 113, 114, 115, 117 & 118: Turn off all breakers to heater. Allow heater to cool down by running cold water through the heater for approx. 5 minutes. Measure the ohms on each temperature sensor and wire by placing the ohm-meter probes on the control board where the red and green wires are connected to the spade terminals, (Refer to theComponent Testing Table for expected values). If there is a low reading (20 ohms or less), further test the suspected wires and temperature sensor individually to determine which is at fault. Replace the wire if there is no continuity. If the temperature sensor has a low ohm reading (20 ohms or less), pull off the red cap to the temperature sensor exposing the threaded stem. While holding the base of the temperature sensor with a small wrench, so it doesn’t move, turn the stem _ turn with a pair of pliers. Check the ohm reading again. If it is still low, turn the stem another _ turn until a good reading is achieved. If the ohm reading doesn’t change, see Temperature sensor Replacement in the Removal and Repair section. Perform the Matching Procedure after adjusting or replacing the temperature sensor. - 127 code: Turn off all power to the heater and ohm the heating elements. Refer to the Component Testing Table for expected ohm readings. If a heating element is bad, there will be no continuity or an infinite ohm reading (the meter may display "no reading" or "open"). See the Removal and Repair section for heating element replacement.
SYMPTOMS/CODES	PROBABLE CAUSES	CORRECTIVE ACTIONS
Water Runs Hot and Then Cold POSSIBLE CODES: NONE 124 127 & 142	- Water lines reversed - High temperature shut-down	- 127 & 142 codes: Turn on the hot water at a faucet. At the heater, if the outlet pipe (on the left) feels cold and the inlet pipe (on the right) feels hot or warm, then the water lines are reversed. Reconnect the water lines so that the hot water line is connected to the outlet fitting and the cold water line is connected to the inlet fitting. This may need to be done by a licensed contractor. - 124 code: This code is triggered when the temperature of the water is more than 10 degrees higher than the set-point at any of the temperature sensors. Typically, this occurs in two chamber heaters when the hot water is shut off abruptly and latent heat builds up in the chamber. Also, it may occur in a four chamber heater used in circulating systems and booster applications, because additional heated water is entering the chamber from the inlet side. This increases the chances of latent heat build-up when the water is abruptly shut-off. The 124 code should clear after the hot water clears the temperature sensors or the heater cools down. If the 124 doesn’t clear or the heater does not turn on and the 124 code persists, call Microtherm for further assistance.
Solid Red LED	Analog control board Digital control board	If the LED is solid red and there are two LED’s, the control board is an older version analog control, made prior to May, 1999. The diagnostic codes do not apply to the analog control. Call Microtherm, Inc. for troubleshooting procedure. Turn off all power to the heater and wait 30 seconds. Then turn on the power. If the LED remains solid red and doesn’t flash, then see Replacing the Board in theRemoval and Repair section. Replace the control board and perform the Matching Procedure.
LED Does Not Come On	Breaker(s) at main panel or sub-panel No Voltage Incorrect wiring Bad LED Bad control board	- Check / reset breakers — most models have multiple power circuits (refer to heater specifications). Verify that the breakers marked for the heater are actually the breakers serving the heater. Check for power at the lugs. Refer to the Component Testing Table for proper voltage measurements at the lugs. - If breakers are on and there is no power at the lugs, it may be possible the electrical wiring is out-of phase to one or more of the incoming power circuits. Turn off all power to the heater and re-wire the circuits until all circuits are measuring 208 to 240 volts across each pair of lugs, L1 & L2. It is recommended that this be done by a licensed contractor. - With all the power on to the heater, and the water running full flow, take amp readings on each red or black heating element wire (refer to the Component Testing Table for expected amp readings). If there are amps measured through all the individual heating element wires, then the LED may be bad. Make sure the light is not being obscured by sun glare or a bright room. Also, activate the audible by removing one of the brown wires from the board and pressing the blue button. If the audible produces the 122 code, then the board is functioning properly. However, if the amp readings through the heating element wires are all zero, then see replacing the control board in theRemoval and Repair section. Replace the control board and perform the Matching Procedure. - Turn off all power to the heater and wait 30 seconds, then turn on the power. If the LED does not come on, see Replacing the Control Board in the Removal and Repair section. Replace the control board and perform the Matching Procedure.

TANKLESS WATER HEATER

TROUBLESHOOTING