Boiler Frost Protection

[Alfie25]

Looking at new boilers I've been reading about frost protection, which as an example, activates when the system water drops to 8 degrees. The boiler then fires up, circulates the system water and heats it to 20 degrees.

In general, on a combi boiler does this mean that the whole of the system water (including the rads of course) gets heated to 20 degrees? Or is there some sort of bypass (with valves) inside the combi boiler itself that ensure that it's just the boiler itself that doesn't freeze, rather than all pipework as well?

 

[ianmcd]

The most common way is for the boiler to go into HW mode but as no HW is being run then the boiler gets to temp very quickly,but this only protects the boiler, it is not a big job however to wire in a system frost stat with a pipe stat on the return which will protect the whole system, basically the frost stat activates at a low temp say your suggested 8 degrees and once the pipe stat on the return from the system reaches whatever you set it to, usuallly 40 degrees then the boiler will switch off