Wiring for UFH and Immersion tank

[gmpiper1]

I have a question for a more experienced electrician.. I've installed UFH in both floors of my house.. the plumber has installed a zone valve at each manifold ie one up and one down for the heating... My question is that in the airing cupboard the immersion has 2 zone vavlves coming off of it.. Obviously one for HW but why would we need the other for the central heating as IVe already got one at each manifold?? any insight would be appreciated!

 

[richy3333]

I know the unit you mean as a customer has had his fail recently, but I'd ask the plumber. It's not a sparkies job to necessarily know how the system works from a plumbing perspective, so long as the units are wired up correctly?

 

[snowhead]

1 of the valves is a safety feature, powered open and fails shut, connected to the safety cut out stat on the cylinder.
It's a requirement of using an unvented to stop the hot water overheating to potentially dangerous temperatures.

Assuming it is unvented??