Frost Stat

[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 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.

 

[Harry Bloomfield]

What sort of frost stat is it, most are adjustable.

 

[DotComMatrix]

It is a Honeywell Froststat. I do not know the exact model number but it looks like this one, https://s3-eu-west-1.amazonaws.com/hbfile/pdf/KE4016.pdf

These can be adjusted from 3 to 20 degrees it seems. It has never been adjusted in past few years. It has only been randomly firing up recently, when it has gone a little cooler, but certainly not freezing temperatures yet.

 

[Harry Bloomfield]

It is a Honeywell Froststat. I do not know the exact model number but it looks like this one, https://s3-eu-west-1.amazonaws.com/hbfile/pdf/KE4016.pdf

These can be adjusted from 3 to 20 degrees it seems. It has never been adjusted in past few years. It has only been randomly firing up recently, when it has gone a little cooler, but certainly not freezing temperatures yet.

Well, take the cover off and check what temperature it is set at and report back. It's not even nearly cold at the moment, so it shouldn't be triggering the heating. Try setting it to minimum and then see if the boiler still fires. Normally a frost stat will be installed in the coldest part of the house, that any part of the heating system is installed in, and set to 5C.

Be aware that some boilers include a their own frost protection, built in.

 

[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?

Do you know if the Potterton Suprima has built in frost protection?

As ever, thanks for any help.

 

[Deleted member 267285]

Which Suprima? There’s been a few. Also how long would you say it’s firing up for? Could be a faulty motorised valve and these can trigger the boiler to fire up.

 

[Harry Bloomfield]

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

Some boilers 'exercise' themselves every now and against, to prevent them seizing up - mine does it.

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

You don't need to open it up, just take the round tamper cover off, to check the temperature setting.

 

[Londoner2]

I used to have a frost on a WB combi boiler in at outbuilding, when temps were freezing it used to fire the boiler up, now knowing it can get cold during nights i set the pipe stat lower and it used to fire for under 10 mins and switch off every hour. I done this to prevent gas bills being excessive.

We dont have this setup anymore as new boiler is inside now, but looking back gas bills werent that high in the end.,

 

[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.