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Activity A | Thermistors Troubleshooting
Each heater is equipped with two thermistors (see image above). One located on the inlet side (yellow wire)
and one located on the outlet side (red wire). The function of the thermistors is to measure the incoming
and outgoing water temperature and keep it within 1 to 2 degrees (+ or -) of the set temp shown on the LED
display. If the thermistors fail, the heater will still activate, however the control board will not send power to
the elements. Follow these steps to test the thermistors. This activity should take 3 – 7 minutes.
Turn off breaker
1. Once breaker is off, turn round knob to ensure no power is at unit. Board should not light up if
correct breaker is off.
2. If board does illuminate the correct breaker was not turned off.
Unscrew front cover of unit.
3. In order to remove the front cover you will need to unscrew 4 phillip head screws located on
each corner of the cover.
4. Two screws located on top of cover facing up and two screws located on the bottom of cover
facing down. .
Locate white plastic cover covering control board and remove.
5. Cover is located on the upper right had side of unit and secured with 4 Philips head screws. One
in each corner.
Locate thermistor on control board (see above image 6 & 12)
6. Disconnect inlet and outlet thermistors from control board. (See below image)
7. Both wire are quick connect style. To disconnect, lightly pull wires until unplugged.
8. Inlet yellow
9. Outlet is red
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