Frost Stat replacement?

[DotComMatrix]

My boiler suddenly seems to come on at random times for a few minutes throughout the day and night. It is a Potterton Suprima in garage.

I suspect the Honeywell Frost Stat has become faulty, it doesn't currently seem cold enough for the frost stat to kick in.

I'm guessing the pipe stat is okay, as boiler does shutdown after 10 minutes give or take.

Does it sound like just replacing the Frost Stat could fix this problem, or is there something else I've overlooked?

Thanks for any help.

 

[Chuck]

You can easily confirm / eliminate it as the cause by disconnecting it for a day or so to see if the problem stops and then restarts when you reconnect it. Only attempt this if you are confident your knowledge of electricity at mains voltages is sufficient to do so safely. If in doubt, use an electrician.

 

[DotComMatrix]

I've yet to open it up, but from googling it looks like the froststat will have 4 wires inside.

Would disconnecting these 4 wires disable the Frost stat? Would the boiler still work for central heating and water or would this disable the whole boiler too?

Thanks for the advice.

 

[ShaunCorbs]

3 or 4 wire you will just need to disconnect the wire in terminal 3 and put a choc block / make safe

Obviously turn the power off to the system before working on it

 

[DotComMatrix]

The boiler never randomly turned on during the summer, so it suggests to me it is weather/temp related.

When I have both hot water / central heating timers turned off, is the frost stat the only thing that can turn a boiler on?

I'm tempted to just buy another frost stat to swap over and test, if I'm gonna be opening it up anyway. Are Honeywell frost stats interchangeable?

As ever, thanks for any help.

 

[ShaunCorbs]

Yes or sticky port valve

There cheap enough and yes easy to swap over

 

[DotComMatrix]

Okay, I've come back to report that all seems well with my boiler now, after replacing the froststat (set to 5 degrees).

Thanks to everyone who took the time to offer any suggestions, in particular the tip about how only the froststat or a faulty motorized port valve can turn on the heating when timer is off.

Our valve was changed around 3 years ago so I was quietly confident it wasn't that, which meant it could only be the froststat.

 

[Ben-gee]

Testing frost stat first would have been “better” but with your inside knowledge on the valve - well done on a successful repair 🙂