When hot water is switched on, some radiators heat up

[suddy]

When I put the timer Hot water switch on to heat the water for an hour (CH switch is off), I am not sure why this happens, but, 2 or 3 of the radiators on the ground floor heat up and 1 radiator upstairs.

Any reason why this would happen ?
I have a Saniflow Indirect unvented system.
Ta.

 

[Youllneverguess]

Zone valve letting by.

 

[suddy]

In lamens terms, is that simply the 'motorised valve in line with the CH pipe that is opening when it shouldn't ?

Could it be that the wiring for this is the wrong way round as, it is a pretty new valve.

There are two types ... a blue plastic covered one and the plain galvanised metal ones. What is the difference. We have one of each.

Thanks

 

[45yearsagasman]

It's probably not opening, but letting by because the valve has not shut off 100%, either caused by system debris on valve seat or valve is seizing up a bit.
The valves are identical in how they work but by different makers.
Probably Honeywells originally, from your description.
The one that controls your heating is the one that requires attention.
The blue one is not BG by any chance?