York HP Series Service Manual page 100

16.4.4 Open or short circuit of temperature sensor diagnosis and solution (E4/E5/F1/F2/F3)
Error Code
Malfunction conditions
Potential causes
Trouble shooting:
E4/E5/F1/F2/F3
If the sampling voltage is lower than 0.06V or higher than 4.94V,
the LED displays a failure.
Wiring mistake
●
Faulty sensor
●
Faulty PCB
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