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Postby DPERRY » Thu Dec 23, 2010 4:47 pm

We have a Heatline combi boiler C24/28, we had a frozen pipe on the outside tap, everything was fine until then, now the boiler works for central heating but the hot water is only luke warm then goes to cold and the boiler switches off. We have found that the water will stay hot if we put the cold water tap on. Someone has suggested that it could be the Domestic hot water sensor but they are only guessing and said we should replace this first because its the cheapest, but we don't want to spend loads of money with trial and error replacements. There are no flashing lights on the boiler stating problems. everything is work other than the hot water. We have had a heater on it just in case it was frozen but still remains the same. Condensing pipe not frozen either.
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Postby jim the plumb » Tue Jan 04, 2011 11:49 am

If the heating is fine then the fault lies with the hot water controls.

I'm thinking if there are no flashing lights then it is a flow sensor fault - the boiler doesn't know the tap is running so it does nothing.

The fault could be intermittent - the flow sensor is failing, 'not failed' so it works every so often.

The part about running a cold tap as well as a hot tap would slow the tap water through the boiler. I don't really get this bit as it would affect the flow through the flow sensor - making it worse.

Without seeing the boiler I'd go for DHW flow sensor.

HTH jimbo
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Postby htg engineer » Tue Jan 04, 2011 7:34 pm

Sorry never touched a Heatline boiler. Do they have a diaphragm ? if yes then it could be stretched or split.

If it was the sensor or anything else for that matter the water wouldn't get hot when the cold tap is running.

When running the cold tap the increase in flow could be enough to keep the hot water going.

If not check/strip & clean/renew DHW flow switch.

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