Boiler cuts out when running hot water

Question

Whenever we run the hot tap for more than a minute the boiler cuts out and the hot water goes cold. It restarts fine but then does it again. What's causing this?

Sam · Answer

There could be a couple of reasons for this, in my experience and the most common fault, this would be a blocked plate heat exchanger. The boiler is cutting out because it can’t move the hot water through the boiler fast enough and is overheating.

Stuart · Answer

Hi Abdul. This is most commonly an overheating issue, and the boiler is cutting out to prevent further damage. This could be a blockage, or water supply issue i.e. a faulty pump.

Daniel · Answer

It’s mainly plate heat exchanger that causes this problem but in other cases it can be diverter valve.

David · Answer

If it’s a combi boiler the there’s probably sludge built up and slightly blocked the plate heat exchanger.
That part possibly needs replacing and the system power flushed

Michael · Answer

If It's a combination boiler it maybe that the flat plate heat exchanger is blocked and will need replacing/flushing out with chemicals

Chris · Answer

Possibly the plate to plate heat exchanger had debris inside leading it to over heat. It'll cut out then cool down then start up again.

Ali · Answer

This could be caused by a faulty plate heat exchanger, flow sensor, diverter valve, overheating, or poor water flow. A qualified engineer can diagnose the issue and recommend the correct repair.

Deepak · Answer

Is this combination boiler? If yes, plate heat exchanger. If not, further investigation is required.

Boiler cuts out when running hot water

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