E50 Fault – Baxi or Potterton boilers
An E50 fault on a Baxi or Potterton boiler relates to a domestic hot water temperature sensor. It is quite uncommon and isn’t readily found in the boiler manuals.
What is an E50 fault?
An E50 fault is caused by the hot water sensor going out of calibration.
The control board in the boiler expects to get a resistance reading from the hot water sensor. The resistance changes depending on how hot the water is.
When the sensor becomes faulty the resistance reading is outside the expected range. The control board doesn’t like this reading and a E50 fault is displayed.
The hot water sensor is screwed into the left hand manifold. It sits it the stream of the mains water after heating so it needs to be sealed using a washer.
Before starting:
- You must be gas safe registered to work on boilers.
- You must safely isolate the electric and the mains water.
- The most common cause of E50 is a faulty hot water sensor.
- It can also be a damaged harness (the wires that go to the sensor).
- A faulty PCB can also give this fault.
How do I know the sensor is faulty?
The only way to test a sensor is with:
- a multimeter set to resistance
- a thermometer so you know its temperature.
If you don’t know the temperature then you can’t know the resistance its supposed to be.
The chart below shows roughly what the resistance should be:
How to fix an E50 fault
To rectify this fault the sensor and seal should be replaced by a competent gas safe registered engineer.
The gas safe engineer would turn the water off and isolate the boiler electrics. Then they would pull off the green lead on the sensor.
Open a hot tap to release the water pressure then close it again to hold the water in the pipework.
Using a small adjustable spanner unscrew the sensor from the pocket. Some water will leak out but it shouldn’t be under pressure. There is a cut out under the sensor that a spanner fits through.
Keep a towel or a small tray ready to catch any drips.
Fit the washer to the sensor and screw back into the boiler. Tighten it up but not too much as they can snap if tightened too much.
Reattach the lead, turn on the water and turn the power back on.
After running the hot water the E50 fault should not come back. The water should be hot from the taps.
The E50 Fault is still there.
- PCB fault
- Wiring harness fault
- The new sensor is faulty.
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