Boiler on too long

[Jilly]

This boiler (Baxi105E) switches on and remains on in cold weather. It cannot be turned off even with the control turned down to '1' (minimum). We have suspected the froststat but we don't know a diddleysquat about it. Anyone help please?

 

[Toddyplumb]

If it is the frost stat it kicks in at 5 degrees and stays on untill the flow temperature reaches 30 degrees. If its doing this its fine .
If it isnt you need to get an engineer to look at it