My Vaillant ECOmax VUW 286 EH combi condenser is giving central
heating but no hot water.

About 8 years old, working fine until early this year when it suddenly
stopped supplying HW. Demanding hot water for the shower, kitchen sink
and bathroom taps the HW would become tepid but not hot and the
radiators would become warm. To get HW you must close the CH valve and
switch the boiler to HW only.

A diverter valve problem then?
Replaced the diverter valve with a brand new one (£14 on ebay), no
change.

A controller board problem then?
There are 22 volts DC at the diverter valve solenoid when HW is
demanded and enough magnetic force to hold a large screwdriver in
place against gravity.

A faulty diaphragm?
The diaphragm is new with the valve and I removed the copper pipe
which connects the diaphragm to the low pressure side of the pump and
it is clear of blockages.

So now I'm stuck, I can't think of what else to try (except email
Vaillant, which I just did) any suggestions?

--
bweebar

On Sun, 10 Jun 2007 20:59:55 +0100, bweebar wrote:

My Vaillant ECOmax VUW 286 EH combi condenser is giving central
heating but no hot water.

About 8 years old, working fine until early this year when it suddenly
stopped supplying HW. Demanding hot water for the shower, kitchen sink
and bathroom taps the HW would become tepid but not hot and the
radiators would become warm. To get HW you must close the CH valve and
switch the boiler to HW only.

A diverter valve problem then?
Replaced the diverter valve with a brand new one (£14 on ebay), no
change.

A controller board problem then?
There are 22 volts DC at the diverter valve solenoid when HW is
demanded and enough magnetic force to hold a large screwdriver in
place against gravity.

A faulty diaphragm?
The diaphragm is new with the valve and I removed the copper pipe
which connects the diaphragm to the low pressure side of the pump and
it is clear of blockages.

So now I'm stuck, I can't think of what else to try (except email
Vaillant, which I just did) any suggestions?


Is there enough flow of DHW water to make the diaphragm move the valve
fully?
I'm not familiar with this specific model.
The problem IS the diverter valve from the symptoms you describe. The
root of its problems is what is not clear.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Sun, 10 Jun 2007 22:35:28 +0000 (UTC), Ed Sirett
wrote:

Is there enough flow of DHW water to make the diaphragm move the valve
fully?
I'm not familiar with this specific model.
The problem IS the diverter valve from the symptoms you describe. The
root of its problems is what is not clear.

Thanks for replying.

The manual is available for download he
http://www.gasaid.co.uk/manualinfo.php?id=250
1.5MB .pdf

Do you mean the flow as in the amount of water out of the taps? A bath
still takes the same amount of time to fill and a hot shower is still
as it always has been (with the CH service valve closed).

Yes, it all points to a problem with the diverter components but the
actual valve unit is new and having replaced it, the old one didn't
seem to be in a poor condition. The system has always had inhibitor in
it and the radiators get hot as expected. The old valve moves freely
between positions under finger pressure, no stiffness at all and the
old diaphragm looks intact.

I measured 22v at the solenoid (at the solenoid terminals as well as
at the connector on the main controller board) which seems an
appropriate value for a working board. It switches on with demand for
hot water and off when the taps are closed again.

Yet for some reason, it's not diverting and the only other thing I can
see that could cause that is the pressure tube that connects the
diaphragm to the inlet side of the pump. I took the tube out
completely and made sure it was clear of obstructions. Does the
diaphragm need bleeding or priming to work?

--
bweebar

On Mon, 11 Jun 2007 00:36:42 +0100, bweebar wrote:

On Sun, 10 Jun 2007 22:35:28 +0000 (UTC), Ed Sirett
wrote:

Is there enough flow of DHW water to make the diaphragm move the valve
fully?
I'm not familiar with this specific model.
The problem IS the diverter valve from the symptoms you describe. The
root of its problems is what is not clear.

Thanks for replying.

The manual is available for download he
http://www.gasaid.co.uk/manualinfo.php?id=250
1.5MB .pdf

Do you mean the flow as in the amount of water out of the taps? A bath
still takes the same amount of time to fill and a hot shower is still
as it always has been (with the CH service valve closed).

Yes, it all points to a problem with the diverter components but the
actual valve unit is new and having replaced it, the old one didn't
seem to be in a poor condition. The system has always had inhibitor in
it and the radiators get hot as expected. The old valve moves freely
between positions under finger pressure, no stiffness at all and the
old diaphragm looks intact.

I measured 22v at the solenoid (at the solenoid terminals as well as
at the connector on the main controller board) which seems an
appropriate value for a working board. It switches on with demand for
hot water and off when the taps are closed again.

Yet for some reason, it's not diverting and the only other thing I can
see that could cause that is the pressure tube that connects the
diaphragm to the inlet side of the pump. I took the tube out
completely and made sure it was clear of obstructions. Does the
diaphragm need bleeding or priming to work?


Could the secondary heat exchanger be blocked?
You could simply make it Vaillant's problem they'll sort it by replacing
everything till it works.!


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

On Mon, 11 Jun 2007 17:27:40 +0000 (UTC), Ed Sirett
wrote:

Could the secondary heat exchanger be blocked?
You could simply make it Vaillant's problem they'll sort it by replacing
everything till it works.!

Had a reply from Vaillant earlier, they too suggested that the flow
through the DHW heat exchanger might be restricted "causing negative
pressure to the diverter valve" so I'll have a look when I get time.

Thanks again for your input.

--
bweebar

On Mon, 11 Jun 2007 19:29:39 +0100, bweebar wrote:

On Mon, 11 Jun 2007 17:27:40 +0000 (UTC), Ed Sirett
wrote:

Could the secondary heat exchanger be blocked?
You could simply make it Vaillant's problem they'll sort it by replacing
everything till it works.!

Had a reply from Vaillant earlier, they too suggested that the flow
through the DHW heat exchanger might be restricted "causing negative
pressure to the diverter valve" so I'll have a look when I get time.

Had a look today, got the heat exchanger out and flushed it through.
It wasn't severely blocked but there was a constant stream of small,
black flakes (insoluble in water, Viakal, oven cleaner or bleach).

Hosed it through for ten minutes then put it back in and hey presto!
the boiler's diverting again.

--
bweebar