I am going to install a thermostat for frost protection of my CH system mainly because the boiler has now been sited in the garage.
I think putting it in the garage will not do as in the winter the temperature of the garage will not rise significantly and the result will be it will over-ride the room stat settings causing the boiler to short-cycle.
I thought of the hallway particularly on an outside wall so it should detect the as near as damn it the same temp that the garage should experience yet it should switch off once the temp in the hall has risen. My main concern is that the temp inside will drop off much slower when the heating is off compared to the garage and the stat will not not fire up the system quick enough.
I have an Eco Hometec badged (MAN Micromat) combi boiler in the garage. This has built-in frost protection based on the outside temperature (it has a sensor for this) and the return water temperature.
I originally planned to add an external frost thermostat for additional protection, and got the bits. However I haven't connected them up yet, mainly because the boiler doesn't actually have a direct "CH demand" input that I can see - their engineer said I could short out the outside temperature sensor and this would make the boiler think it was minus XX degrees and would force it into firing mode.
Anyway, you need two parts - the actual frost stat and a clip-on pipe thermostat - I think it's called something like a "low limit" stat. When wired together correctly this combination means that the boiler is forced into CH demand mode when BOTH of the following are true :
1) ambient temperature is less than the frost stat setting (about 5 deg C ISTR but probably adjustable in the frost stat)
AND
2) the return temperature (measured by the clip-on pipe thermostat) is below its preset temperature (I'm really guessing now - maybe something like 15 deg C).
So your problem would not happen - the room temperature in the garage doesn't need to rise - it just makes the boiler fire until the water in the pipes/radiators is coming back at a reasonable temperature.
If you get a Honeywell frost stat, the instruction sheet explains all this and the part number of the other pipe stat. Our local PM kept both in stock, so seems like a pipular combination.
You don't need to do that, although I agree it would work.
Have a look at the MHS Boilers web site and download the installation guide for the Strata 1. It will seem quite familiar but rather better. There are some scenarios of different plumbing hookups (most for small commercial use, some for domestic), and there are also wiring diagrams.
Depending on what you have in terms of controls, the inputs and outputs behave differently. For example, the CH demand inputs can either be for a room thermostat or a temperature sensor. The point is that you have to select the correct function code for this and for the operating temperatures. This can be reached via the engineer's menu. I presume you know that this can be reached using access code 21. The functions are better described in the MHS translation.
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