"PM" wrote in message
...

"Andy" wrote in message
...

"Ed Sirett" wrote in message
...
On Tue, 16 Jan 2007 22:39:05 +0000, Andy wrote:

"Chris" wrote in message
ups.com...
My central heating only comes on when the HW circuit is turned on.
With
both off, if I turn on the CH circuit via the programmer, the
motorised
valve turns on and winds open but the boiler does not fire up. If I
then turn on the HW circuit via the programmer the boiler fires up
and
heats HW and CH.

This used to work perfectly until recently. Nothing has (knowingly)
been changed since it was working.
There was a room thermostat but I bypassed this during renovations by
joining both brown wires (L and SL) and insulating the earth and
neutral. This was bypassed long before this fault developed.

I have a Potterton Suprima 60 boiler for CH and HW which are
individually controlled by the programmer.
I have a Myson motorised 2-port valve at the boiler (for CH) and same
next to the upstairs cylinder.

The boiler and programmer are about a year old, the valves etc. were
installed by the previous owner.

A picture of my boiler can be seen here
http://84.203.164.145/boiler.jpg

Does this sound like an electrical or perhaps a PCB problem? The
status
light does not change colour when I turn on the CH alone. Another
thing
that's weird is the reset button doesn't seem to do anything, on my
old
boiler this used reset the boiler if I pressed it when running.

I'd rather not have to get my plumber out if I can avoid it so any
advice would be much appreciated.

Cheers,
Chris.


Actually, belay that diagnosis, I didn't read your post carefully
enough
:0(


I think your original diagnosis is correct the 2 port valve is stuck
half
open, enough that the rads warm up but not enough to close the conacts
to
fire the boiler.

Ah, well I've learned something the I wasn't sure about the way the
two-port valve signalled the boiler it was allowed to fire.

You should have a lever to manually open the valve. See if this fires the
CH
when the HW is off.

Not sure about Myson but on a Honeywell 2 port that does not work. Only the
synchron motor can do that and a failure mode I have experienced is that a
failing synchron motor opens the valve but does not operate the contacts.

Jim A