This unit is primarily designed for use with van mounted WFP systems,.. mostly aimed at hot users, but to some degree it will work on cold systems.
The idea is that you would fit a male quick connect into the top of your tank, and when you finish work on a cold frosty evening, you simply click the end of your hose reel onto this connector & switch on this unit.
The unit has a temp probe with 2mtrs of cable, so you simply position the probe near/against the bit of equipment you are most worried about being damaged by frost (Your RO/Pump etc).
When the temp hits 4C, this unit will start powering your wfp pump & circulating water around your entire system, hose reel included. In a cold system, your tank might be cool,.. but even the little heat that's in in when combined with constant circulation, will keep everything from freezing until the weather becomes really severe.
When this unit is combined with a heater, the water flow would ignite the heater unit & actively warm your system,.. you'd never have to worry about frost again!
Unlike similar units, this one has been designed with a 15 minute reset zone,.. after 15 mins of constant operation, if the temp has not yet risen above 4C, the frost protect unit will cut power to the pump for 30 seconds & then resume. This 30 seconds of inactivity allows a heater a 2nd chance to ignite on the rare event that it didn't light first try, and it also allows heaters with inbuilt timers like the popular L5's to reset and continue providing heat.
I would like to stress that the use of heaters in a vehicle unattended overnight is something that should not be undertaken if you have the slightest doubt about your systems safety. Only heaters that are externally vented & properly fitted should be used, and even then at your own risk.