Again Roger, thanks for all of your help.

Thats right, it only trips when the CH motorised valve is closed. I
fully opened the by-pass valve, with the CH circuit off, I noticed
that the water wasn't passing through the by-pass valve, massive
temperature difference on either side of the valve. I'm thinking that
this valve may be faulty and is stuck closed (it's not motorised),
should I replace this or is there another method of fix?

Regards

"Roger Mills" wrote in message ...
"Danny" wrote in message
om...
Hi Roger,

Thanks for the info. The pump runs for approx 10 minutes after the
boiler shuts down, I guess this means its wired correctly.

The two valves (one for HW tank, and the other for by-pass) were only
slightly cranked open. My concern for opening the by-pass valve fully
was that the water would simply travel the easiest path, thus reducing
the efficiency of the CH when the motorised valve is actually open.
However I take your point about opening it fully and workng backwards
to find the 'best' position.

With regards to the valve that regulates the water supply to the HW
tank, do you recommend that this be fully open also? Can adjusting
this vavle help to stop my boiler from short-cycling? (I think thats
the correct terminology!)

Regards,

Danny

The valve on the HW circuit is there to balance the flow when the motorised
valves for CH and HW are both on - i.e. to make sure that most of the water
goes to the radiators. You need to find the right position for this, so that
the HW gets hot in a reasonable time without stopping the radiators heating
up quickly. I would experiment with positions around half open - or maybe a
bit less.

Assuming that the boiler only trips when both motorised valves are closed
(i.e. when CH and HW demands are both satisfied) the position of the manual
valve on the HW circuit won't affect this. It only comes into its own when
both motorised valves are open. [If the boiler trips when the HW is still
being heated, this valve definitely needs to be opened more].

Incidentally, "short-cycling" is something different - and not what I
believe you've got. Short cycling is when the boiler runs for a few seconds
at a time and then go off. And then comes on a bit later, and does it all
over again. AIUI, your problem is that the overheat stat trips - and has to
be re-set manually before the boiler will light again. Is this right?

Roger