Central heating problem

[macksmid]

Having problem with my heating system. over the last couple of years have replaced like for like room stat and timer clock.
My problem is when the heating is completely off at the timer the radiators will still come on when just the hot water is selected. Could it have something to do with the diverter valve? do I need a replacement?
This problem has only just started and I think has no relation to the new parts fitted a few years ago?

 

[ollski]

The valve is passing...what make is it?

 

[ChrisR]

Do you mean that when the hw is heating that the rads get warm? If so yes, if you have a 3 port valve it's sticking. (If 2 x 2 ports the CH one's sticking open a bit at least.)

Can you take its head off? Often a leaking spindle leads to binding.

 

[macksmid]

The valve is passing...what make is it?

 

[macksmid]

Thanks all this is my first post so finding my way around. I think the head will come off i will check tomorrow and it's a Myson power extra the system is about 13 years old.
Many thanks