20 11112014GW
Code 31 Troubleshooting Procedure
Burner Thermocouple
1. WARNING: You must be qualified to service gas systems before proceeding. Check low/high
fire manifold pressures for proper settings. See gas pressure setting procedure located
under the front cover of unit in the technical data sheet. In addition, can be found in the
product’s service manual. Set manifold pressures per instructions for your altitude.
2. Verify all dip switches are set to the proper position on the PC board. See technical data
sheet for proper settings at your altitude.
3. Measure milli-volt (mV) reading of burner thermocouple. The thermocouple milli-volt
range should be between 20 to 27 mV under normal combustion. If the reading exceeds
30 milli-volts or is less than 8 milli volts the unit will go into a code 31.
If the thermocouple mV output is above 30 mV during combustion that indicates the
unit may be over fired. WARNING: You must be qualified to service gas systems before
proceeding. Verify your high fire manifold pressures. If gas pressures are found to be
within specifications, remove burner manifold and burners. Check for blockage between
heat exchanger fins. If clogged clean all debris from fins or replace heat exchanger.
If the thermocouple reading is below 8 mV during combustion that indicates low gas
pressure or low Btu content gas. In other words the thermocouple is not senses a high
enough temperature inside the combustion chamber due to pressures or gas issues.
Verify your forced low fire gas pressure. If pressure is found to be within specifications,
contact Rinnai tech support for assistance.
4. Replace thermocouple.
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