Error Code 35; Error Code 38; Error Code 51 - Rheem RTG2-42 Troubleshooting Manual

Error Code 35

Explanation: Improper Thermistor Connections. Check to make sure that all thermistor
connections are good and in the proper locations. There are four thermistors on the tankless unit.
They are the ambient air thermistor, cold water inlet, hot water outlet and heat exchanger
thermistor. At a minimum check the following:
1. Check thermistor wiring and Molex connections.
2. Check and clean ambient air temperature thermistor.
3. There is no troubleshooting for this error code other than a visual inspection.
4. If a thermistor fails resistance check, then use that error code to process.
5. If all thermistors check good, then replace the board as first resolution.

Error Code 38

Explanation: Oxygen Depletion Sensor has malfunctioned. The sensor itself is not responding to
the printed circuit board. At a minimum check the following:
1. Check sensor wiring and Molex connections at connector Q.
Is there any
milivolt current
at Connector
Q?
Yes
Replace Burner Assembly

Error Code 51

Explanation: Gas Inlet Solenoid Valve fault. At a minimum check the following:
3. Check gas valve wiring harnesses for loose or damage terminals
4. Check connections to the circuit board are tight.
Cycle the heater two times by turning off – then on – at 10 second intervals.
Is there any
remaining
flame thru the
view window?
No
Display Maintenance Information 0y (flame rod status)
SVC 810 Tankless Troubleshooting Manual
No
Replace Printed Circuit Board
Light main burner and run for two
minutes. Measure milivolt current at
Connector Q between the Red and White
wires: 8 to 30 mV DC
Yes
Replace Gas Control Assembly
57