Grant Condensing boiler switches on temporarily

Gwynston

Our outdoor boiler occasionally randomly switches on for a minute or so outside of normal operating hours.

I know there is a design feature to do this as a frost guard to warm itself up in cold weather, but it seems to do it when it's not that cold out, and even in the summer occasionally. I mentioned it to the service man who came recently and he was none the wiser, and didn't seem to know about the location of the frost stat or whether that might be the problem. He did run a OFTEC report which didn't show up any issues as far as I'm aware.

Anyone have any insight?

jimf

if you have motorised valves for zoning your system this would be first place to check

the microswitch can stick causing above issue

can also be caused by frost stat but not as common as above

jimf

just to add if its a grant vortex it will have a factory fitted frost stat

if its a euroflame a stat will have been wired in at install if at all

imho your service guy should easily be able to identify a frost stat and its location

Gwynston

Thanks for the reply - it's a Grant Vortex.

But I don't understand how the zoning motorised valves could cause it? In the summer, if both the upstairs and downstairs thermostats are set so that the heating shouldn't come on and the hot water setting is not active, why would the boiler kick in (only for a minute or two) in the middle of the day?

declan b

There is a micro switch in the motorised valve.if its faulty it can send a live to the boiler.If all zones are off and the boiler comes on ,it should either be a faulty micro switch in the motorised valve or a faulty frost stat[ if the temperature is above 4 degrees}

declan b

It might be an intermittent fault but it may not be.

Try this test

a/Set the stat to minimum 55/60 degrees.With all zones turned off. Go to the boiler turn up stat and see what you get..

b/Before you turn on the boiler in the morning. Check the pipes on the top of the boiler and see if the pipes are above 60 degrees approx

Gwynston

Thanks - I'll give it a try.

Writingskin

I've had a similar issue with my outdoor boiler. It can be frustrating. Sometimes, it might be a glitch in the thermostat or timer. It's worth checking those settings.

Gwynston

So what did you have to do to fix it?