They don’t come with a frost stat setup like a Grippa or the like , but they do have a timer you can set to come on and off overnight , however in order to use this the water pump would have to be left on all night as the heater cannot turn the water pump on by itself !
This is why I just do it manually 2 hours before bed as and when I see a cold snap coming , again this is dependant if you can rely on the workers remembering to turn them off !