Cylinder stat that works the opposite way to the standard ones

[manikki]

Does anyone know if I can buy such a thing as a Cylinder stat that works the opposite way to the standard ones?
I have a very basic heating system off a solid fuel back boiler plus an electric immersion in tank for back up. When the pump is off the water only heats up. When we turn on the pump the radiators also get warm. For years we have operated this manually, turning it on when needed and off before bed. It occurred to me that if we could have a thermostatic switch that sensed when the tank was up to temperature and turned the pump on then turned it off when the temperature dropped below a certain temperature, we could go to bed knowing the pump would go off in the night.
Does such a thing exist? Or can anyone suggest any other way to do it?

 

[Echo the husky]

Almost all cylinder stats have this option, just wire to common and normally closed, instead of the usual common and normally open. For most stats this is terminals C and 2

 

[Dan Robinson]

A standard one will do this. But why not run both together?

 

[Roger928]

Or can anyone suggest any other way to do it?

The usual set up (and best) on a gravity system is hi-lo stats sensing the flow and return temperatures. When the return rises high enough the pump is switched on and excess heat goes to the radiators.
An injector T (two pipe system) will be fitted which aids flow around the cylinder coil.