cylinder stat required if already have thermostatic cylinder value?

fletch

I got a BER assessment done recently, and the assessor advised that I needed to get 2 more TRVs and a hot water cylinder stat in order to improve my BER (which will allow me get a cheaper mortgage rate). So I got the TRVs sorted but the plumber wasn't sure if/how the cylinder stat could be wired into my existing (Nest) heating system. Furthermore he wasn't really sure if it was entirely necessary since I already have a thermostatic cylinder valve on the hot water flow going into the tank (This seems fairly dumb though and just controls the water temp going into the tank, but doesn't feed back information to the boiler to stop it firing if the tank is hot enough).

My question is, do I really need a cylinder stat if I already have a thermostatic valve? It seems like the cylinder stat would be slightly redundant?

Cylinder stat

Thermostatic Cylinder Valve

youtheman

A cylinder stat is an electrical device that normally activates an actuated valve, and the actuated valve has a limit switch which gives an electrical signal to the boiler to start/stop. So you can have it so that the boiler is only on for heating hot water (i.e. zone valve suppling radiators is closed and zone valve for hot water open, i.e. summer time). The thermostatic cylinder valve is a mechanical device. Not sure how it is installed. But I think it is fitted to a system that might not be zoned, so that you have the option to close the feed to the cylinder while the boiler is heating the house via the radiators. But it cannot be used to just heat hot water only, i.e. you can have radiators on and hot water off, or radiators and hot water on.