Girard Products GSWH-2 Technical Manual page 13

If the temperature of the water displayed at the UCP is nowhere near the temperature of the water coming out of the water
heater you may have a thermistor out of calibration. Check the temperature on the copper pipe where the output thermistor is
located with a laser thermometer to confirm the temperature.
This issue can also be a result of a mixing of hot and cold water in the plumbing system. The standard plumbing issues that
cause this problem are mixing through a winterization by pass kit or if the valves on the outside shower are turned on and the
outside shower head is turned off.
High temperature incoming water will force the water heater to its lowest BTU's. When this occurs mixing of cold water in
at the faucet will decrease the temperature of the water of the faucet but it will decrease the water flow through the water
heater causing the temperature at the water heater to rise. This higher temperature will show on the UCP.
If the input thermistor is open when the board senses that the flow sensor is on then an E4 fault code will be given
E4: Water Inlet Temperature Probe failure.
An open circuit or short circuit condition is detected: This could be due to an internal failure in the Temperature Probe or to a
faulty connection (Wires)
Thermistor Removal and replacement
Output
thermistor
Input
Thermistor
Turn off the water supply.
Identify input and output thermistors. Remove
compression nut using an 11mm crow foot wrench.
The thermistor is sealed into the water systems
with an O Ring. Reach in with needlenose pliers
and firmly pull thermistor out of the fitting. Do not
damage or discard the O ring.
Remove the wire from the control board.
Reinstall in reverse order.
Check for Water Leaks.
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