Potterton Suprima - CH will only come on when HW is also on

[thedoodydoo]

Hi All

I'm having a bit of a prob with my central heating and wonder if anyone has any ideas.
The boiler is a 6 year old Potterton Suprima 40L and here's an overview of the prob:

If I switch on the central heating, the boiler doesn't light.
If I switch on the hot water the boiler lights straight away.
Once the boiler has been lit by the hot water, if I then switch on the central heating, it works fine and the radiators heat up.
Once the hot water tank's got to the correct temp, the hot water goes off and so then does the heating.

I have to admit that I haven't a clue, so I'd appreciate it if anyone has any suggestions. Thanks for taking the time to read this post, and apologies if I haven't given enough information.

Cheers! - Dave

[Steve the gas]

Hi,

From what info you have given, I suspect you have a motorised valve,(near cylinder/pump) This is your problem. The head needs changing.

Hth

[thedoodydoo]

Hi Steve - thanks v.much for that - you were spot on!
Dave

[RibShack]

Hi all,

Smiliar problem here in fact, but if I turn the CH on, then the RCD board trips out and loses all my electricity to the sockets.

I've got a new 3 way motorised valve, as suggested here - I assume I need to go through the horrible process of draining the whole system before installing it?

Thanks.

[Steve the gas]

Hi,

Not a drain down if you're just replacing motor head.

Hth