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PostPosted: Fri Oct 06, 2017 2:55 am 
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We run oil heating and last year we had a couple of breakdowns due to the boiler shutting down due to the over heat button coming on. Had an engineer come out (via insurance) and he said the boiler is overheating due to the thermostats on the rads. He recommended that we take off a thermostatic valve so the extra heat in the boiler would be expelled through the rad which doesnt have a thermostat on.
Is this correct can this happen???


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PostPosted: Fri Oct 06, 2017 8:08 am 
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Firstly I am not an oil boiler engineer, but the basic principles will be the same as a gas boiler.

The internal boiler thermostat should be controlling the water temperature in the boiler and shutting it off before it reaches high enough to pop the overheat.

But, saying that, it is usual to have one radiator that doesn't have a TRV fitted, the one in the room that has a room thermostat, so it acts as a bypass for the system.

If you have TRV's on all your rads, then the system should have an automatic bypass fitted somewhere.

If it has been ok for years and only just stared doing this, then things like the pump and general system cleanliness/sludge/scaling need checking.

What make and model is it for when the oil guys come on and have a look?

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PostPosted: Fri Oct 06, 2017 11:48 am 
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I have just been to look at my father-in-laws central heating, and it transpires the micro-switch in the motorised valve was stuck closed, so central heating boiler was firing up with no water flowing and it still did not trigger the over heat cut out, the water temperature control was regulating the temperature. OK his was gas, but it would be unusual for any central heating boiler or immersion heater with the exception of solid fuel not to have a thermostat and a over heat cut out. It would seem the central heatings boiler internal thermostat is faulty.

There does seem to be some debate over bypass valves and leaving one radiator with no TRV. The problem I have found with mothers system there is nothing to explain how the boiler works, with non condensate the boiler simply switches on and off, however with condensate boilers the return water temperature is important, too hot and it can't capture the latent heat of evaporation, there are two methods to ensure cool enough return water, one is alter flame height and second is use a heat store, latter used with solid fuel however condensate boilers with solid fuel is very rare, they are made, but most are DIY jobs.

What I did was to down load the parts list for mothers boiler, it showed certain items which gave me a good idea of how it worked, the bypass valve built into boiler for example, and both output water temperature sensor and cut out. However we can't simply guess, you have to read to see what the manufacturer has used or said in his instructions, without knowing make and model no one can answer your question.


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PostPosted: Fri Oct 06, 2017 12:44 pm 
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gas4you wrote:
Firstly I am not an oil boiler engineer, but the basic principles will be the same as a gas boiler. The internal boiler thermostat should be controlling the water temperature in the boiler and shutting it off before it reaches high enough to pop the overheat.


That's how our's works.

Had this happening very occasionally more or less from new with ours. In the end the overtemp stat went faulty. So could have always been tripping at the wrong temp.
Second time it happened the boiler stat was faulty and the overtemp stat just did it's job.
Of course it was the worst cold weather we've had down here for years!


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PostPosted: Sat Oct 07, 2017 5:06 pm 
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Boiler is a Flowsure combi 10 years+ old


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