It's 30 degrees Celsius outside but heating came on!

[sylviesinc]

We have a Worcester 18/25 oil combi boiler and have it serviced annually. It's about 5 years old. We leave the digital thermostat set at 15 or so and, of course, while the air temperature is higher than that, the heating doesn't come on. Last night we were sweltering in 30 degrees. I went into the bathroom and was shocked to find that the radiator was red hot! The one in the passage nearby, which is always the first to fire up, was the same. None of the other radiators in the house felt warm.

Any ideas why this happened please? I have turned the heating off completely for now but need to know what the fault is. Thanks.

 

[kidgreen61]

When you say the "heating came on", do you mean the boiler fired, or was it just that a rad felt warm?

Do you have a hot water storage cylinder in the house?

 

[sylviesinc]

It's a combi boiler so we don't have a hot water cylinder as such. The water is heated in the boiler unit as and when needed, as I understand it. The boiler fires up as and when hot water is required, so we don't really notice it coming on and going off any more, however when I felt the boiler unit, it did feel warmer than usual so it must have been sending hot water to the radiators.....and believe me when I say that two radiators were VERY HOT, not merely warm. Do you think the thermostat is faulty?

 

[kidgreen61]

It sounds as though the boiler is sending hot water around the heating system when it is firing for hot water.

Methinks you will need to call someone out to it

 

[Burnerman]

These boilers have a diverter valve lurking inside......and as the name suggests, it can divert the boilers heat to either the hot water supply or the heating circuit.
If it fails, then the hot water produced can make its way into the heating circuit, instead of that being completely closed off.
John

 

[stardanny]

Diverter valve inside combi letting by. Might happen on pre heat for hot water.

Switch it back on, starting from cold, leave heating off and run hot water on a taps, does first radiator get hot slowly?

Need a boiler engineer to fix it.

Daniel.

 

[sylviesinc]

Many thanks guys. We have an idea of what it can be now and the annual service is due in a couple of months time, so it looks like we'll have to ask our friendly boiler engineer to visit early and fix it. I hope it's not an expensive part!!!