Head scratching heating problem

[JamesE]

Hi guys

Been having a problem with the mother in laws heating. All has been well since she brought the house seven years ago. Then sometime last week the heating started firing up on its own even with programmer off. When it does this there is no control over anything. You can cycle through the programmer with no response. ( lifestyle lp112 ) then she noticed when she had the hot water on the rads would become hot so all pointed to the 3 way mid position valve. Drayton. So i changed the head and it has fixed the problem. But the original problem still exists. Ive noticed that when the last thing to be on was the heating this is when it randomly comes on anytime of day or night. When the last thing on was water then it doesn't do it. Ive also changed the programmer and there is no room stat so I'm a bit stuck on this one. Desperately seeking your expert knowledge. Thanks guys

 

[Ermintrude]

Possibly guts of valve or a loose connection / stray live?

 

[gassafe]

The power goes through the cylinder stat to the heating on a y plan system I think, maybe that could be worth changing as its a relatively cheap item - is it an old one on there?

what boiler is it? Could it be an internal boiler fault? Similar to old Worcester ri's that fired the boiler due to a stray boltage from the control system...

 

[gasmanrob]

Frost or pipe stat?

 

[JamesE]

Thanks for the speedy replies guys. From what i understand the power goes from the programmer to the 3 way valve which tells the boiler to fire up. It only comes on when the last thing on was the heating. So the valve stays on the H when switched off. Which is causing it to keep coming on so im guessing its a problem live maybe ? But if it is then surely it would remain on constantly. The boiler is a potterton suprima 40. The pcb was changed about two years ago because it kept locking out. Could it be the same again ?

 

[Vee]

Drayton valves are carp. Replace the valve body too, not just the head as it's likely to be sticking.

 

[JamesE]

Ive already changed the grey actuator. Just clips on and off. So your suggesting to change the valve itself too and see if that does the trick ?