Vaillant firing when no call for heat

So are you suggesting that its got a sensor that does not like to be in a sealed enclosure? are there not any ventilation holes in it? Brian

Brian Gaff wrote on 21/07/2018 :

No, I am not suggesting that - the cupboard is purely cosmetic, open top and bottom, plenty of space at the sides and front. I built it to accept a much larger boiler, long ago.

My original thoughts were, that the boiler would run a purge every so often just to exercise itself - pumps etc., if it hadn't been called for a while. That was the sort of brief cycling I was witnessing.

Many of the Vaillant boilers seem to have similar facilities - basically to exercise fans, pumps, valves etc to make sure they don't seize during periods of low use.

John Rumm used his keyboard to write :

The Vaillant help desk tec didn't seem to suggest, or realise it had such a facility. It seemed to be once per day, but at no particular timing. HW is triggered once per day at 16:20.

My Vaillant has a feature designed to minimise the delay between calling for hot water, and delivering it. It tries to keep the internal temperature around 60-70C. So will fire every so often.

It can be enabled/disabled from the front panel where the DHW temperature is set.

I have an open vented HW and heating circuits by choice. So this is just being used as a simple boiler system.

I have a feeling, its mentioned somewhere in the documentation for mine...

That's usually on the 800 series combi boilers.

The person that fitted my Valliant forgot to remove the 24V link when using mains ON. This causes the boiler to cycle. I had quite a hard time explaining the mistake to the "engineer" that came to investigate the problem after I spotted the link still being in place. It would have been easier for me to have opened it up and looked myself in the first place.

Does the system have a wireless thermostat?

John Rumm laid this down on his screen :

If it is in my documentation, I have been unable to spot it.

To be fair, I would be surprised if it didn't exercise things regularly.

Graham. used his keyboard to write :

A wireless room stat., yes..

Consider the possibility that the receiver is picking up an ON command occasionly from another device nearby.

My radiators came on mysteriously in the night on two occasions during the recent heat wave The pairing was done via 8 bit DIP switches in the stat and receiver, since I changed the code it seems to be OK. The original setting was not the manufacturer default (all OFF) I thought that would be asking for trouble.