Frost Stat Question

[ChizzDoha]

Hi all - first time poster and have zero knowledge about boilers/heating systems, so please be gentle
Our boiler (Baxi EcoBlue Advance 19 Heat Condensing Boiler) is located in an attached garage with a separate Honeywell frost stat wired in next to it. In very cold weather, the frost stat is coming on and heating up the radiators/hot water in the house for long periods of time, several times a night.
Our central heating programmer/timer is a Honeywell ST 6400 (C) system and it seems that whatever programme was on last before the frost stat kicks in, whether it be the hot water or heating, is what will come on when the stat is activated, even when we put them both in the "off" position on the timer. (The timer is usually set in the "once" position for both heating and hot water and we put the heating only on in the afternoon/evening on the "continuous" mode and switch it off when we feel the house is warm enough).
Ideally we do not want neither the hot water or heating on when we are in bed.
Do we need a pipe stat fitted to the boiler to prevent the radiators coming on? or could it be a problem with the diverter valve in the boiler that is making the heating or hot water come on?
Do I contact Baxi? (as the boiler is still under warranty) or the Heating Engineer who fitted the boiler?
I did contact 2 other local Heating/Plumbing companies who both told me that it was normal for the heating to come on (for prolonged periods) when the frost stat kicks in and that I didn't need a pipe stat. Reading some posts on this forum, the advice is that I do.
Many thanks in advance!

 

[muggles]

Your boiler doesn't have a diverter valve - that's in your airing cupboard. Yes, a pipe thermostat on the return pipe and wired into the frost stat is what you need

 

[ChizzDoha]

Many thanks

 

[Harry Bloomfield]

A frost stat will ensure the area where it is fitted, is kept above 5C. A pipe stat on the return, close to the boiler, will ensure your heating system doesn't freeze. It's pointless fitting a frost stat in an unheated area, because the heating can never warm that up - there you would use a pipe stat. If you have a normally heated area, which is at risk of freezing, then you would install a frost stat there. Sometimes it is sensible precaution to have both fitted. Modern boilers include built in frost protection, but usually only to prevent damage to the boiler itself.

 

[ericmark]

How it is plumbed and wired is down to the installer, but normally the wall thermostat will open a motorised valve which once open works a micro switch which then turns on boiler and pump, but the frost stat works direct onto boiler and pump without opening the motorised valve, so the by-pass valve opens allowing water to circulate without going through radiators.

However it seems this is not always the case, with my mothers bosch boiler there was a by-pass valve inside the boiler and also one outside the boiler, and although in her case it did not matter which opened, if the boilers own opens with your set up the pipes could freeze, so as it is clearly safe as water is circulating stopping pipes freezing.

Stopping rooms over heating is easy, simply fit a programmable TRV head, but you really need to talk to the installer, he knows what it should do, and if I or anyone else gives advice which results in a frozen pipe that would not be good, so talk to your heating engineer.

 

[ChizzDoha]

Thank you both for your replies. The guy who installed the boiler is coming round tomorrow.

 

[ChizzDoha]

Update on the situation: Heating Engineer who installed the boiler sent his Electrician around. He checked the Frost Stat and said it was set too high at 5 degrees and turned it down to 3 degrees. I asked if he could fit a pipe stat and he said that it was not needed...that he had never needed to fit one in 30 years.
I said that I understood the Frost Stat should be at 5 degrees (according to what I have a read on many forums) and that it should be fitted in tandem with a pipe stat, otherwise the heating will stay on until the garage reaches the Frost Stat temp, which could be a long time (costing us a lot more in gas bills).
The guy basically said he had told me situation (was quite rude and bothered that I asked him questions), that by adjusting the FS to 3 degrees I would have no more issues and left (didn't charge us to adjust the frost stat switch).

I had shown him the Baxi EcoBlue Advance 19 Heat Installation Manual which states : "The following arrangement is rec'd: Utilise a room frost stat in conjunction with a pipe thermostat. The pipe stat should be located on the primary return close to the boiler".

My question to the experts on this forum is: having spoken to 2 heating/plumbing companies on the phone a while ago and this guy in person, they say that a pipe stat is not needed and that the heating should come on (for however long!) to protect the system from freezing up.
Why are some Heating Engineers adverse to fitting pipe stats in conjunction with the frost stat? Is it too tricky a job? Do they not know how to do it? Not a big enough job to warrant them going out to you?
I don't understand when it states in the manual that it is recommended and most of you guys say it is.

Many thanks

 

[Harry Bloomfield]

My question to the experts on this forum is: having spoken to 2 heating/plumbing companies on the phone a while ago and this guy in person, they say that a pipe stat is not needed and that the heating should come on (for however long!) to protect the system from freezing up.
Why are some Heating Engineers adverse to fitting pipe stats in conjunction with the frost stat? Is it too tricky a job? Do they not know how to do it? Not a big enough job to warrant them going out to you?
I don't understand when it states in the manual that it is recommended and most of you guys say it is.

You are correct, in that with just a room frost stat, the space that it is in has to rise above the stats temperature to turn off. If the space is an unheated space, then it will rely upon the small amount of heat lost through the boiler case and the pipe work, to switch off - the result being what you are experiencing, the heating running all night. You need a pipe stat, absolutely no doubt about it. Chase the installers again and insist they either fit a pipe stat or get in touch with Trading Standards.

 

[stem]

What tosh. The two parts can be purchased together as kit.

I've never fitted a frost thermostat without a pipe stat when the boiler is in an unheated area. As you point out the heating will run continually if there is no source of heat connected to the heating system in the area where the boiler is located to raise the ambient temperature and switch it off. Meaning if the frost stat is triggered, your home could be being heated to its daytime temperature all night.

The pipe stat just ensures that warm water is circulating around the system to prevent the water freezing.

The two thermostats are wired in series, meaning that both have to be calling for heat for the frost protection to kick in.

 

[ianmcd]

As @stem says absolute rubbish you have to fit a pipe stat with the frost stat , hardly a major job

 

[ChizzDoha]

Many thanks for your replies. Really don't want the same guy coming around again, as I was a bit upset with the way he spoke to me.
Guess i have to keep calling around local recommended Heating Engineers until someone will agree to fit the pipe stat.
Are they reluctant to touch another Heating Engineer's work, e.g. for if it has been wired incorrectly or something?

 

[ianmcd]

To be honest far too many so called heating engineers are boiler slingers and wouldnt know what you are talking about, if you say what area you are in maybe someone on here could recommend someone in your area

 

[ChizzDoha]

Sounds like it! Any recommendations are welcome...I am in Warrington, Cheshire
Btw, does someone have to be gas registered in order to fit a pipe stat, as technically they are not working on the boiler itself? (not that my husband nor I would try to do this ourselves, however simple it may be....)
Thanks again

 

[ianmcd]

Btw, does someone have to be gas registered in order to fit a pipe stat

Nope no qualifications needed, and an easy DIY job to be honest

 

[MJN]

To be honest far too many so called heating engineers are boiler slingers and wouldnt know what you are talking about, if you say what area you are in maybe someone on here could recommend someone in your area

I was going to have a rant about incompetent tradesmen but your post has made me think more positively...

I reckon to be competent you have to be interested, and so a forum like this with some on that do this for a living happy to be talking about their line of work 'after hours' is a clear sign of interest and so it seems an ideal place to find what is likely a competent tradesman.