having a problem with a motorised valve that feeds the hot water
cylinder - a couple of times lately it's stuck and i get no hot water
- the lever is on auto - as soon as i move it to manual the everything
starts to work again - putting it back to auto then works again for
any number days. A couple of questions - apart from getting a plumber
to change the valve is there anything a novice diyer like me can do to
remedy the problem and what's the consequences of leaving it switched
Thanks in advance
In an earlier contribution to this discussion,
I'm assuming that you have a separate valve for the CH, and that that is ok.
The motor in your valve is switched on by the programmer and cylinder stat,
so that the valve opens when there is a HW demand, and closes when the
demand is satisfied. Once the valve is open, some contacts in the actuator
close and switch on the boiler and pump. This is obviously not always
happening in your case. The valve is either not opening at all, or it's
opening but not far enough for these contacts to close. Operating the manual
lever opens the valve and enables the contacts to close.
Leaving it permanently in the manual position will mean that the boiler and
pump will run all the time, and the water will get too hot because the valve
won't close when the cylinder stat is satisfied - so *don't* do that!
You could try removing the actuator from the valve and turning the valve
spindle backwards and forwards a number of times, and then replacing the
actuator. That might just free it sufficiently to make it work more
If , when you remove the actuator, you find that the valve does turn freely
over its full range, there may be a problem with the actuator itself, but
that sounds less likely.
I only have experience of Honeywell. The sympoms you describe are
consistent with the synchron motor having lost the oomph to fully open the
valve and then drive the contacts closed, though with a Honewell switching
to manual doesn't normally make the contacts. Is it possible that the CH
was also calling for heat?
If its a Honeywell the head can be replaced which doesn't require draining
down but does require the wiring centre to be accessed. It's possible you
could takle the task safely as a novice diyer - but only if you are
confident you can isolate the mains to the wiring centre.
Once you get more confidence the synchron motors are replaceable.
On mine it won't keep the boiler and pump running but yes it usually
means that the HW will be heated(or cooled) when demand for CH is also
called for but if you set your boiler output to a lower temp there'
little risk of the water getting "too hot". I suspect the motor in
the valve is at fault. One from screwfix should do it.
In that case, remove the valve cover (1 screw, just loosen it a turn and the
lid will slide off), and then IIRC you will see 2 screws that fasten the
head to the valve.
Remove those then lift off the head and you should be able to easily rotate
the valve itself and feel for any "stiction".
....I bet it's the servo taht's the problem!
On Tue, 15 Jan 2008 11:07:27 GMT Roger wrote :
I have had a number of motor failures, never a body. The guy who
invented the MV must have had a little probably explaining to his
fellow engineers the validity of a design that relies on stalling an
electric motor and keeping in this state for ages at a time.