E50 fault on Potterton or Baxi boiler.

An E50 fault on a Baxi or Potterton boiler 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 which changes depending on how hot the water is.

When the sensor becomes faulty the resistance reading is outside the expected range which the control board doesn’t like resulting in an E50 fault.

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.

A picture of where a hot water sensor is located in a taxi or potterton boiler
The hot water sensor

A picture of a hot water sensor in a bag
The hot water sensor

How to fix an E50 fault

To rectify this fault the sensor and seal should be replaced by a competent gas safe registered engineer.

With the water turned off and the boiler electrics isolated the gas safe engineer 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 and the water should be hot from the taps.

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