"Ed Sirett" wrote in message n.co.uk...
On Tue, 11 Nov 2003 03:37:10 +0000, Ian Nutt wrote:

"Ed Sirett" wrote in message on.co.uk...
On Mon, 10 Nov 2003 10:46:15 +0000, Ian Nutt wrote:

"Ed Sirett" wrote in message on.co.uk...
On Sun, 09 Nov 2003 05:22:31 +0000, Ian Nutt wrote:

"Ed Sirett" wrote in message on.co.uk...
On Sat, 08 Nov 2003 09:50:44 +0000, Ian Nutt wrote:

I have a Vaillant combi boiler and seem to have a problem with the
diverter valve. The hot water only comes on when the heating is on. I
have taken the diverter valve out of the boiler to study it and can
see that the diaphram is supposed to push up a pin that forces a
hammer to fall and make a contact that ignites the burner and diverts
water into the hot tap system.

When I turn the hot water tap on you can see the hammer try to move
down to make the switch contact, but it does not have the energy. It
would seem that there is not enough pressure to push it hard enough.

Does anyone out there understand what i'm talking about, or, even
better, know what the problem might be?

Which model? They work by very different mechanisms.

Ed - thanks for getting back. I don't know! Cannot see a model number
written anywhere and have no documents on it. Do you know how I can
identify it?

Please describe the general appearance - eg. grey/black/beige control
panel. Permanent pilot or electronic ignition? Fan assisted flue or
balanced natural draught flue?

Anyway from the description is it most likely a split diaphragm in the
water flow sensor.

If you look around and perhaps remove or swing-down a panel you will
likely find the model type and rating plate.


Ed,

I have taken the right hand side panel off and there is no
identification plate visible anywhere, just various stickers with
nothing that looks like a serial number. The pump has 'Type VP5'
written on it, but I assume this refers to the pump.

The control panel is black, with green dials and a pressure gauge
bottom right. There are 4 dials (on/off/relight, water temp, ch temp,
function setting) and 7 indicator lights that light up green to
indicate when the burner is on etc. It is electronic ignition and
naturally vented flued I think.

Aha we have a vaillant VUW this is the model comes between the VCW and the
latest Turbomax+ series. It is forced flue with a fan. IIRC.

In this model the DHW is fired from the microswitch mounted on the
right hand side of the diverter valve/flow valve.
The water flow diaphragm operates directly on the diverter valve and the
microswitch.

You could have a problem if the diverter valve is stuck/sticky.

Exactly right! The microswitch is a tiny fellow which makes the
circuit when this white plastic hammer I keep mentioning pushes down
on it.

How do I ensure the diverter valve isn't sticky? Any tips?

Thanks again for your continuing attention.

There may be an inadequate flow of water to correctly operate the valve.
There may be a split diaphragm in the valve.
The diverter valve might be too stiff to move easily enough:
i) failed lubrication
ii) sludge etc. in pirmary
iii) mechanical failure (unlikely)

The micro switch could be iffy - not enough to show when you operate it
with a finger but enough when operated by the valves.

I have bought a new diaphragm and will fit that on Saturday - ill let you know!