Boiler pump running when no heat being called for

[floob]

I'm finding that occasionally the boiler pump will be running when no radiator is calling for heat (and the boiler is outputting none). I havent really timed it, but its just for a few minutes I think.
Its not directly after heat has been called, but seemingly at random.

Do some boilers run it periodically for any purpose?

 

[Incrisis]

My combi boiler has an internal hot water tank so there is instant hot water when called for, the boiler will often fire and run for a few minutes to keep the tank at a certain temp.
That seems to be the only part of my boiler that wants to work properly at the moment though

 

[CBW]

Make and model of boiler would be a good start.

 

[Harry Bloomfield]

Do some boilers run it periodically for any purpose?

My Vaillant occasionally runs its fan and I would also assume the pump too briefly, even when there is no call for heat and no call displayed on the LCD display. The assumption is that is does this regularly, to ensure nothing gets the chance to seize. It just does a quick run for a few seconds as it would when doing a purge cycle before stopping then restarting and firing - except it doesn't take this final step.

 

[floob]

Make and model of boiler would be a good start.

Its a Viessmann 100-W B1KF 35kw combi.

 

[floob]

My combi boiler has an internal hot water tank so there is instant hot water when called for, the boiler will often fire and run for a few minutes to keep the tank at a certain temp.
That seems to be the only part of my boiler that wants to work properly at the moment though

Thanks, that could be it I suppose, but I'm pretty sure the 'pre-heat' function isnt live as its in Eco mode.

 

[floob]

My Vaillant occasionally runs its fan and I would also assume the pump too briefly, even when there is no call for heat and no call displayed on the LCD display. The assumption is that is does this regularly, to ensure nothing gets the chance to seize. It just does a quick run for a few seconds as it would when doing a purge cycle before stopping then restarting and firing - except it doesn't take this final step.

Thanks, maybe thats it. I'll see if I get a reply from Viessmann.

 

[CBW]

Could a link have been left In for heating? Do you have any zone valves?

 

[floob]

Could a link have been left In for heating? Do you have any zone valves?

When you say Zone valves - is that like the Tado SRVs?
I have these:
https://www.tado.com/gb-en/smart-radiator-thermostat-overview

Last night it went on at 23:50 for about 3 mins. No radiator called for heat nor was any tap used in the previous hour.

 

[CBW]

No, I meant 2 port zone valves. Your trv’s may have a frost stat, it could still be the preheat, or there could be a pump run cycle, Intergas boilers have it.

 

[floob]

Viessmann have said:

"The pump will run on after a water demand for 3 minutes, and after a heating demand for a minute .
Occasionally if there has been no operation the boiler may do a system check also "

So I'm thinking its these 'system checks' that I hear at odd times.