Thanks guys.
If it is a little rubber ball there's a possibility then, that it could have deformed allowing water to go through both outlets, irrespective of what position the valve is in.
Anyhow, tried Mandate's suggestion - both pipe to cylinder and pipe to rads became hot when the valve was manually turned to HW only. So, I think I'm going to order a complete new valve and have a go at it myself. All will not be lost if it doesn't fix the problem, I will have of gained a little experience as I've never done any plumbing work.
I've been doing a lot of reading up on here (great forum) and I'm pretty confidant I can drain down the system, fit new valve and re fill. Fingers crossed!
If it is a little rubber ball there's a possibility then, that it could have deformed allowing water to go through both outlets, irrespective of what position the valve is in.
Anyhow, tried Mandate's suggestion - both pipe to cylinder and pipe to rads became hot when the valve was manually turned to HW only. So, I think I'm going to order a complete new valve and have a go at it myself. All will not be lost if it doesn't fix the problem, I will have of gained a little experience as I've never done any plumbing work.
I've been doing a lot of reading up on here (great forum) and I'm pretty confidant I can drain down the system, fit new valve and re fill. Fingers crossed!