Do I need Honeywell frost stat

berlumberley · Jan 18, 2012

Hello all. My first post.
I have a Vaillant eco tec boiler in the garage with built in frost stat. There is also a Honeywell frost stat inside the garage wired up to the boiler. The boiler is coming on when the temperature dips but all radiators get very hot and stay on for ages (days) even when temp raises. They eventually do shut off but it's costing a fortune. I think that the plumber may have "fixed" the frost stat when he rewired the heating system in the summer because we didn't have this problem last winter (and it was very cold for weeks on end). Do I need the external frost stat if the boiler has an internal one and if not can I just disconnect it. Many thanks.

jtsplumbing · Jan 18, 2012

Sounds like its not wired up right ! should not need externel frost stat, the one in the boiler will only protect the boiler, the room stat in the house will protect the house. probable old frost stat is left over from older boiler.

tipintim · Jan 18, 2012

Open the stat cover and see what he has set it at. May be too high.
Being in the garage, I would keep it. IMHO

berlumberley · Jan 18, 2012

It is set to 5 degrees and probably is kicking in about there. Just gets too hot and doesnt switch off and causes the rads to get hotter than they would normally do. I would have thought that it would act as protect only and cut out as soon as it was protected rather than make us all sweat! If it's the wiring I'd better get someone to have a look. Thanks.

tipintim · Jan 18, 2012

Sounds that boiler isnt being controlled by frost stat or room stat. Your running on boiler stat temperature. Needs to be looked at mate.

jtsplumbing · Jan 18, 2012

Why not ring Vaillant and ask what they think, but it needs sorting!!

Anton · Jan 18, 2012

Or you could use a pipe stat wired in with the external frost stat, this would help to protect the pipework but at lower temperatures.

Heating-eng · Jan 18, 2012

Sounds like frost stat is set too high.. Turn it down to lowest setting.. If that doesn't work you could remove it.. The frost stat may not be needed ,depends how much pipework is in garage and if it is lagged.