Frost protection thermostat advice please.

[Scotty1980]

Hi there,
Wonder if anyone could kindly identify from the picture below if the thermostat on the left is a pipe stat used on the return for the boiler frost protection? and if so what temp it should be set at. Or is this for something different?
I have a boiler installed in my garage and recently during the cold weather the frost protection thermostat has been turning the heating on and heating all the radiators. I noticed that when I turned the dial on the left down to around 55 the frost protection fires up the boiler only for a few mins before it seems happy and turns back to standby. However with this dial up at 80 (where it was) the boiler is cycling on and off every few minutes and all the radiators run red hot all night allowing me no control over them even when timer and controls are all off.
Any help would be greatly appreciated. Many thanks.

 

[Chuck]

Difficult to be sure what it is without a bit more detail about the system but it is not a conventional frost protection thermostat.

If it is on the return to the boiler it is probably intended to shut down the boiler when the difference between the flow and the return temperature drops, indicating that the TRVs in the house are mainly off and the system is 'bypassing'. If you have a condensing boiler, for maximum efficiency in cold weather, you probably want the return thermostat set at about 55°C and the flow temperature thermostat at about 75°C. If this is pumping out too much heat, try 40 and 60 respectively.

These sorts of controls are normally inside the boiler these days.

If you are not sure how your system should work, get a heating engineer to check that it is set up and performing correctly.

 

[Ric2013]

Is it possible that the pipe stat is just a simple pipe stat and it is monitoring the pipe temperature and there is another frost stat monitoring the temperature elsewhere, and the two are wired in series? Not saying I'm sure, but I'm a-wond'ring.

Thus IF the pipe stat senses the pipe is cold AND IF the frost stat senses that its location (loft?) is cold (below 5°?) THEN the boiler will fire and run the radiators.

This would explain the boiler only firing for a few minutes and then shutting down again if the pipe stat is set to 55°C.

 

[SimonG]

Pipe stat should be on return. Set at about 40. It Should be wired in series with the frost stat. Frost stat set at about 5.
Temp drops to 5 and frost stat kicks boiler and pump in. Runs until return pipe hits 40 which then cuts power to frost stat and boiler shuts down. Residual heat should stop cycling too frequently.
Also fit frost stat onto a small piece of ply to lift it off the cold wall.