I have a Drayton 3 port valve on my vented system and can't get hot water only for the summer, it heats up radiators as well. I assume it is jammed open or blocked. Worked fine last summer; system is about 6 years old.
There are 3 positions for the front switch W-M-H. I remember it was at M but is now at H and I can't seem to coax it over. Don't want to force it in case it breaks off. Does this matter ? is this the problem ?
Have looked on Drayton web site but it offers no technical advice.