In an earlier contribution to this discussion,
Michael Kilpatrick wrote:

Despite being a clever design, they couldn't be more obtuse, could
they?
I'm trying to work out why, this morning, the central heating came on
despite the timer control being set to off and the thermostat turned
down. Hot water was fine, I think, and the thermostat on the cylinder
is certainly activating the boiler when appropriate. Controller is
standard old thing with a timer and "off-cont-twice-on" settings for
HW and CH.

It sounds as if the valve has stuck in the mid position. When that happens,
the boiler will fire (and the pump will run) whenever there is a demand from
the HW stat - but water will flow round *both* the HW and CH circuits.

I assume it must be the 3-port valve (Honeywell Sundial Y plan), but
once all the pipes everywhere are hot it seems actually rather hard to
test it without waiting for everything to cool down again in order to
see where heat is being delivered when I mess about with the controls.


If I think the motor has gone, then if I disconnect all the wires
should it stay in "how water only" mode?


It depends on exactly what's happened. If the 'wet' part of the valve has
seized, nothing you do to the actuator (the electrical part) will make any
difference. If the actuator has simply got confused (and it *can* happen!),
powering it down completely - at the FCU which feeds the whole system, not
just at the programmer - may 're-boot' it and make it work properly again.
[If you need some help to determine which it is, come back.]

Also, I can't find out what the manual override lever on the valve is
for!!! Is it supposed to set it to "heating only", "hot water only",
or "both on"??

It moves the valve - against the return spring - to the mid (both on)
position, but not all the way to the CH-only position. It makes it easier to
fill the system with water by opening both circuits at the same time. If
it's working properly you'll feel quite a lot of resistance from the spring
and gears as you open the valve, and if you then let go of the lever, you
will hear the gears whirring as the spring closes the valve.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!