Heating's off but rads are on

[philprice]

I have an Ideal HE 30 boiler. The central heating is switched off but this week the radiators have started heating up when we run the domestic hot water.

We also have an H 3 fault code flashing on the boiler, but not constantly. When this is flashing it sounds as though the pump or something is running but the burner light is not on.

When the fault code is flashing we can run the hot water for 10 seconds or so and this seems to clear the fault, so we assume something somewhere is sticking. H3 fault code relates to the DHW thermistor. Would a faulty thermistor cause these problems or is it something else??

Any ideas?

 

[Agile]

I think your boiler has two DHW thermistors, one to measure the hot water temperature and the other to determine a demand.

It sounds as if the diverter is sticking.

The first thing I would do is to depower the boiler for an hour and then measure the resistance of all the sensors.

If they are correct then I would for the moment give my attention to the diverter valve.

Tony