Intermittent Heating and Lukewarm Water - Combi Boiler

[cwcw]

Happy New Year.

Over the last couple of weeks our combi boiler has started playing up again. One symptom is that the heating sometimes thinks it is hot enough when it isn't. I can tell from the click on the room thermostat dial that the room is not up to temperature when it does this. The radiators seem to heat up and then the boiler stops firing and seems to quietly hum as though it is on but thinks it doesn't need to fire up. Turning it on and off again, or turning the radiator thermostat on the boiler up further, kicks it back into life again for a while. Previously the radiator thermostat on the boiler was around 6 and the hot water thermostat 7, and this worked fine for ages. Now, they are both cranked right up to the maximum of 9.

The other symptom is the hot water is only luke warm. This seems to be more of a problem when the heating is on - it's on a timer so a shower when the heating timer is off is ok, but when it's on then it's lukewarm at best.

Does anyone know what these symptoms could be pointing too? We have only recently had a new temperature sensor fitted because it was faulty and causing the diagnostic light to flash intermittently. This time there are no diagnostic lights. Boiler is around 11 years old, Alpha CB24X.

 

[twgas]

Has it been serviced lately?

 

[cwcw]

Has it been serviced lately?

Yes, serviced when the new temp sensor was fitted, about a month ago. It has been serviced regularly as far as we know, but belonged to previous owners for most of its life.

 

[ianmcd]

Do you know which temp sensor was changed ? your boiler has 2 and they are both the same a DHW one and a Primary one, I usually change both at the same time as they are not that expensive but are prone to failing

 

[cwcw]

Don't know which temperature sensor was changed.

Boiler is not working at all now though, great timing! It is doing everything it should be apart from firing up/ igniting. Presumably there's no way to manually ignite a combi boiler to put us on until tomorrow?