Code(s)

Probable Causes/

Conditions

Investigative & Corrective Action

111

112

113

114

115

Inlet Temperature sensor (TH-IN)

Temperature sensor #1 (TH-1)

Temperature sensor #2 (TH-2)

Temperature sensor #3 (TH-3)

Temperature sensor #4 (TH-4)

Codes 111 through 115 were designed to identify an individual temperature sensor with a problem. They will be associated with either a 117 or 118 code.

Turn off all the power to the heater. Cool down the heater by running the water for approx. 5 minutes. Ohm the temperature sensor circuit, that was identified by the self diagnostic code, by placing the ohm meter probes on the red and green terminal connections on the control board. Compare the ohm reading to the ohm readings of the other temperature sensors.

Refer to the Component Testing Table for expected readings. Check the red and green wires for continuity. As needed, replace any bad wires or adjust the temperature sensor.

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 (the inlet temperature sensor requires unbolting the red wire).

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Code(s)

Probable Causes/

Conditions

Investigative & Corrective Action

111

112

113

114

115

CONTINUED...

Refer to the Component Testing Table for expected readings. Check the red and green wires for continuity. As needed, replace any bad wires or adjust the temperature sensor.

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 (the inlet temperature sensor requires unbolting the red wire).

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 Matching Procedure after adjusting or replacing the temperature sensor.

117

Not Used

(Shorted Temperature sensor)

The 117 code will appear with another temperature sensor code, such as 111, 112, 113, 114 or 115. This code was designed to indicate that there is a short in the temperature sensor or in the temperature sensor circuit identified. Check the red and green wires for continuity and refer to the same Corrective Action above for the temperature sensor codes.

118

Open Temperature sensor

Typically, the 118 code will appear with another temperature sensor code, such as 111, 112, 113, 114 or 115. This code was designed to indicate that the temperature sensor circuit identified is open. Check the red and green wires for continuity and refer to the same Corrective Action above for the temperature sensor codes.

121

Disable Switch Open or Missing

The disable trace is cut, damaged or corroded on the control board. Refer to the Removal & Repair section to replace the control board.

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Code(s)

Probable Causes/

Conditions

Investigative & Corrective Action

122

High Limit Switch Open/ Tripped

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. If a temperature sensor problem is found and corrected, perform the Matching Procedure.

123

Water Level Detect Shutdown

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.

124

High Temperature Shutdown

The 124 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 and the heater doesn’t turn on, call Microtherm for further assistance.

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Code(s)

Probable Causes/

Conditions

Investigative & Corrective Action

126

Moisture Detect (Water Leak)

Immediately shut off all power to the heater. 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. Tighten or replace leaking part or seal according to the specifications found in the Removal and Repair section of this manual.

Using a hair dryer, dry down the board and the moisture detect sensor before turning on the power to the heater.

If the code persists, turn off the power and use the hair dryer to dry the sensor again and recheck for leaks. If the heater is dry and no leaks can be found, the sensor could be shorted due to corrosion. As a temporarily measure, remove or disable the sensor by removing the two yellow wires from the control board. The 126 code should go away, but do not leave the heater in this configuration. Replace the sensor so as not to eliminate this important safety feature.

127

Breaker(s) at main panel or sub-panel

Incorrect wiring

Loose connection

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.

With breakers on, check for power at the lugs. Refer to the Component Testing Table for proper voltage measurements 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.

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.

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Code(s)

Probable Causes/

Conditions

Investigative & Corrective Action

127

CONTINUED....

Heater undersized for the application

Bad heating element

(Verify no current during operation first. The following procedure will help isolate the problem to an element vs say another part of the heating circuit such as the relay)

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 model ratings and flow rate specifications.

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.

132

High Mains Voltage

Slightly higher voltage than nominally specified will not affect the performance. Sustained voltages higher than 10% above the nominal rating should be corrected so as not to damage the heater. Code will clear when voltage returns to nominal range.

133

Low Mains Voltage

Low voltage may reduce heating capacity of the heater. Sustained voltages below 20% of the nominal rating may cause the heater to shutdown. Code will clear when voltage returns to nominal range.

134

(Future)

Not Used

(Bad Element / Circuit #1)

(Future)

135

(Future)

Not Used

(Bad Element / Circuit #2)

(Future)

136

(Future)

Not Used

(Bad Element / Circuit #3)

(Future)

137

(Future)

Not Used

(Bad Element / Circuit #4)

(Future)

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Code(s)

Probable Causes/

Conditions

Investigative & Corrective Action

142

Data Reading Error (A/D Converter Error)

The heater needs to be reset. Turn off all breakers to the heater for approx. Wait 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 the Removal and Repair section.