I too am having problems - but am not certain whether it is the valve
(ACL LIfestyle 779H 340 3OLO 3 port mid position valve), the control
panel or the PCB board in the boiler. I have contacted both
manufacturers of the control panel and the valve and of course, each
says that the others equipment is at fault!
The problem is occasional and includes:
1. Manual CH override did not work. So, tried HW override which did
work. Turned this off after a few minutes and then tried CH override
again. This time is worked.
2. On another occasion, CH override was utilised. The HW then came on
automically (clcok setting). However, when teh HW went off (clock
setting) it also took the CH off with it - even though the CH override
light on the controller remained on.
3. CH did not come on at the programmed time - although the thermostat
clicked on in the hall. Also, the CH light lit up on the control panel.
CH would only come on if HW and CH overrides were put on together.
As I said, Drayton think the control panel must be at fault whereas
Danfoss (control panel)advise that the motorised valve is the most
likely cause of teh problem. So, an independent view would be much
appreciated before I fork out a lot of cash.

By the way, the valve mentioend above must be replaced in its entirity.
I am advised that the replacement is the MA1-779-3 (28mm).

Thanks

Colin