Frost Protection

[AlwaysLearning]

I had one of those "bloody hell!" moments over the weekend.

I had reason to drop by one of my offices on Sunday morning. I rarely go there at weekends because it's empty and the heating is off. When I went in, it slowly dawned on me that it wasn't cold. It was normal working temperature. Crossed my mind the cleaners had been in and pinged the boost. Bins were still full, so ruled that out.

Then I twigged that it was icy outside and the frost stat had turned the boiler on. I'd never thought much about it before, but I checked over the boiler wiring just out of curiosity. That's when I realised there wasn't a pipe stat. Boiler goes on and pretty much stays on until the air warms up in March. Bloody hell!!

So, I'm going to strap a Honeywell L641B1004 stat to the return pipe and splice it in series with the frost stat. Not a big job.

Couple of questions. The boiler (~130+kW) sits in a detached boiler house maybe 4m away from the main building. There's a frost stat mounted outside the boiler house. It's pretty old, Maclaren Type GAF if that means anything to anyone. It's a metal box. When it triggers, it simply bypasses the timer and fires up the heating. It isn't easily adjustable as far as I can see so I'll leave it be. However, I have heard mention that the frost stat should be inside the boiler house, not outside, so it only kicks in when the air around the boiler is cold. If it's outside it could trigger falsely if it gets wind chilled or the housing gets wet with rain and freezes. Any thoughts?

Also, what temperature should the pipe stat be set to?

[ericmark]

It depends on all sorts, including if anti-freeze added to coolant, but in a house with internal boiler often around 12 degs C is used one to ensure no cold spots under zero, and two to reduce warm up time. Commercial often electric tracing heating is used.

[AlwaysLearning]

Getting access to the 4m of underground piping to add electrical trace heating would not be practical for the time being. Hence adding a pipe stat.

[gas4you]

It won’t matter where the frost stat is once you have fitted the pipe stat.

Fit the pipe stat in the boiler cupboard and try setting it to 10c. This should stop it firing unnecessarily whilst protecting the system