Rinnai HE Series How To Use Manual page 173

1. Check thermistor wiring harness for loose, broken or damaged connections from thermistor
back to PC board.
2. Turn off water supply to the water heater and drain system down. With no water left in hot
water supply lines remove the thermistor and check for scale build up on thermistor. Clean off
any substance found on this component. Proceed to item #3 below.
3. With water supply still isolated and thermistor removed from unit, check resistance readings of
this component using a volt/ohm meter capable of reading 20K ohms. Set meter to proper
setting for checking 20K ohms and insert meter leads into each end of the thermistor plug. Then
apply heat to the thermistor bulb. You will notice the thermistor resistance reading start to drop
when heat is applied. A simple way to apply heat is to place the thermistor bulb between your
thumb and another finger and apply pressure. The heat from your body will cause the resistance
reading to decrease. If the thermistor reading starts to decrease with heat applied normally
that indicates the component is functioning properly. The resistance reading will increase if ice is
placed against the bulb. Typical resistance values are 11.4 – 14K ohms at 59 degrees ⁰F, 6.4 –
7.7K ohms at 86 ⁰F, 3.6 – 4.5K ohms at 113⁰F, 2.2 – 2.7K at 140 ⁰F or 0.6 – 0.8K at 221 ⁰F.
If thermistor readings are correct re‐install this component ensuring the small O‐ring is still
intact in thermistor well before installation. Place a small amount of grease or lubricant on the
O‐ring to prevent damaging it during installation. Turn water supply back on and check for leaks
around this component. Next re‐fire the unit to see if you still get a code 32. If so, replace the
thermistor.
Code 32 Troubleshooting Procedure
Outgoing Water Temperature Thermistor Fault
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