Whats this stat for?

[Dave Walters]

Having a few problems with my Mistral oil fired system but seem to be getting on top of it now.
Can anyone tell me what this stat is for located in the garage by the boiler. It seems to be set at 21f or -6c ? What use could that be?
Couldn't see how to attach an image but its a basic old dial stat with an anti tamper cover.

 

[Deleted member 120897]

That temperature range and location, it sounds like a frost/pipe thermostat

 

[SimonG]

As above Frost stat, should be wired in with a pipe stat for max efficiency.