Thank-you all for taking the time to respond.
I was only asking the question as the way its worded on Ionics website appears to suggest that you can heat pre-heat to aid with the prevention of frost damage when the temperature drops (perhaps, so i thought, with an inbuilt immersion).
It really is a fantastic bit of kit but unfortunately does not have a 'frost stat' to prevent any damage in sub zero temperatures and can't understand why Ionics have produced a state of the art system IMHO but you have to pop a £20 radiator, or similar, in the back to protect it from damage!
I have an old Heatwave diesel heater which has a stainless steel enclosure. Believe it or not, there isn't that much heat that radiates from the heater enclosure, even when running during the day.
My 650 litre tank is fitted width ways between the wheel arches just forward of the rear axle on my Peugeot Boxer SWB van. This means that I have a usable space between the bulkhead and the tank. This is where I have fitted the diesel heater. I also have a usable space between the rear doors and the tank. This is where the hose reels reside.
When my frost protection linked to my diesel heater activates at 3 degrees, there isn't enough heat from the diesel heater's enclosure to keep the hose reels from freezing up. The core water temperature reaches about 80 degrees before the frost protection deactivates.
I have an 800 watt electric heater that goes in the back of the van. It does to a certain extent influence the temperature at the front of the tank, but the frost protection attached to the heater triggered at 3.40am this morning. The temperature in the heater is 15.6 degrees at 9.00am this morning.
So as per Daz, I wouldn't trust the electric heater to fully protect my diesel heater in a cold snap like we are experiencing now.
Spring Europe to make the Frostat fitted by other suppliers and is an easy add on fit to any diesel heater.
The internal heating circuit of the heater is protected against the cold with antifreeze. But the issue is the second circuit in the plate to plate heat exchangers. The one side will have antifreeze, but the other side that carries the pure water to the brush head doesn't have antifreeze. Its the heat exchangers that the Froststat protects.