In an earlier contribution to this discussion,
Daniel wrote:

Hi Paul,

Thanks for the reply. Ok, to be honest I don't know the diff between
a combi or plain boiler. It's an "Ideal Minimiser SE". The keypad
to control it is a Donfuss FP715. Upstairs in the airing cupboard
there is a Donfuss Motorised Valve.

I'm definately putting on the HW and not the CH. The keypad is easy
to use, and I made sure CH was on "OFF" and I put HW to "ON". I've
been reading in the Google newsgroup archive of uk.d-i-y and some
guys say the motorised valve could be gone (Thats why I mentioned it
above) but I am not sure how to test it. It has a metal lever on it
labeled Auto/Manual, and I moved it over, but it didn't help so I
moved it back to Auto. I've noticed then even with the hot water on,
the radiators are on as I mentioned, and on one side of the motorised
valve (labelled "Central Heating") the pipe is hot, but the other
side (Labelled "Hot Water") the pipe is luke warm.

Any more suggestions? I see a new motorised valve is around £31.00
so I want to be sure it's that, and if it is, can I fit one myself?


First, a bit of education . . .

You have a conventional (not combi) boiler which provides central heating
and stored (not instant) hot water using a Y-plan setup ( see
http://content.honeywell.com/uk/homes/systems.htm)

This uses a mid-position 3-port motorised valve to direct the water from the
boiler either to the radiators or to the heating coil in the hot water
cylinder, or to both at the same time.

In its rest state, the valve gives hot water only. The internal motor inside
the actuator drives it to the mid or CH position, as required. It has a
spring return to bring it back to the HW position when motor current is
removed.

For one reason or another, your valve isn't returning to the HW position.
The valve is actually in two parts - the wet bit with a shaft sticking out
of the top and the actuator (the electrical) bit which rotates the shaft to
direct the water to the right places. The chances are that the wet bit has
partially seized up due to lack of exercise during the summer.

You should be able to remove the actuator from the top of the valve by
undoing a couple of screws (but leave it connected electrically). You will
then see the shaft - which is circular in cross section apart from one flat
bit (making it a bit like a D). You should be able to rotate the shaft
backwards and forwards with finger and thumb - or at any rate using light
pressure with a pair of pliers. If you can't, this is your problem. You may
be able to free it up by turning to and fro with pliers. If you can't, you
will need to replace the wet part of the valve - which involves partially
draining the system.

If the valve is free, but you *still* have no hot water, the actuator could
be faulty - but that is less likely. With the actuator removed from the
valve, test the spring return by moving the lever and then releasing it. You
should see and hear the spring returning it to the rest position. If it
doesn't, the spring is duff. These actualtors do have other modes of
failure - but these usually result in no heating rather than no hot water.
--
Cheers,
Set Square
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