72 NPE Service Manual
4.11.15 Circulation Pump (“A” models only)
Part Check Point
Function
1. Pump operates when using internal or external hot water circulation.
2. Internal circulation will minimize the effect of temperature fluctuations and external circulation delivers hot
water to fixtures quickly resulting in water conservation.
Failure Event Unable to detect or measure water flow rate when the pump is called to operate.
Effects
1. The water heater freezes.
2. Temperature fluctuations when the water heater is set to internal recirculation.
3. Hot water is not quickly available at fixtures when the water heater is set to external recirculation.
Error Code E438
Diagnostic
1. Visual inspection: Check the circulation pump connection wire.
* Check for blocked/clogged water filter.
2. Voltage check: Check range of voltage shown below.
Color/Number
of wires
YELLOW-WHITE
●
ON : AC 96 ~138 V
●
OFF : 0V
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