boiler firing up even when heating + water is off

[suzetommo]

I have a combi boiler + it keeps firing up when the heating + water are off.

It fires up, stays on for a few mins, goes off for a few mins + then does it again. It has been doing it constantly day + night for the past couple of days.

Any ideas why its doing this??

[SpikeyBush]

Mine does that too. Indeed the whole street is the same, identical houses with identical heating systems. I'd be interested to see what others have to say about this.

[boxtops]

Mine does it - temp fluctuates. It fires up too when I turn on the taps on the washbasin. It doesn't seem unusual.

[bizzylizzy]

Is the thermostat set to a certain temperature? Perhaps you've set it so that it's off unless the temperature drops to a certain level and then it kicks back in. As tabathazig says, look at the controls. Sometimes buttons get pressed by accident. Good luck.

[ladybirder]

Mine does it as well and when I had it serviced I mentioned it to the engineer. He said it is supposed to do that but I can't remember why. Soz.

[nungate]

Ours kept turning itself off and on, the plumber said it was the thermister - no I have no idea what it is either but he fixed it and fingers crossed all is well. Check the thermister or get a plumber

[missprim]

Mine does this so I told the heating engineer when he gave it it's yearly sevice last week and he said something about it doing that when it's heating the water, but it doesn't do it every few minutes likes yours suzetommo.

[buildersmate]

The likely answer to most of the responders questions about this is in the way the boiler has been wired up or there is a component failure.
What is happening is that the boiler is wired such that as soon as the temperature in the sealed domestic hot water part of the system falls below the set temperature (typically 70 degrees C) of the boiler, the boiler fires up. This is correct if the domestic hot water is 'calling' for heat, but what is happening is that the boiler should be wired so that this doesn't happen if the domestic hot water part is NOT calling for heat. Otherwise all that is happening is the boiler is 'cycling' - which means it is heating the water in the sealed part of the system heats up to 70, the boiler turns off, the water cools down to say 60 and the boiler starts again to repeats the cycle without any useful heat ever having been taken out.
This is the technical explanation of what is happening - perhaps others can comment on which component in a combi goes kapput for this to occur.
In a non-combi system it is usually a logic wiring fault that causes this.
Definitely worth sorting out - it will cost you a bomb.

[suzetommo]

Thanks for that, I've spoken to Ideal + they are saying its an electrical fault as the burner light is constantly flashing I the status says 'c'.

[dacortin]

My Vaillant Combi does the same. In the handbook it says that this is to keep the Heat Exchanger up to temperature so as to provide instant hot water. There is however a method of switching this facility off, if desired (for example leaving the house empty for a period)