Rinnai HE Series How To Use Manual page 172

1. 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. 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.
Code 31 Troubleshooting Procedure
Burner Thermocouple
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