Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose with
certainty.

For some time we haven't been able to get the DHW to fire when we ran the
shower upstairs - if we opened another HW tap then it would.
Some time after we began to notice the water was getting v hot.
Next thing was that the pilot light would blow out when the water
overheated. After the pilot was relit the DHW would not easily fire again.
We would have to wait until the whole thing cooled down.
During this time the CH seemed to operate OK.
Finally today, we could not get the DHW to fire at all and something had to
be done.

I thought the thermocouple was ok and the pilot problem was linked to the
overheating so I decided to replace the DHW thermostat and check and replace
the diaphragms in the 'water section' and the diverter valve - (I had
previously done this some years ago when we were getting no dhw and I
discovered a tear in one of the diaphragms.)
Well, when I got home from the Parts centre I found they had given me an NTC
sensor not the DHW thermostat - but I changed this anyway.
I changed both the diaphragms - although the old ones looked ok and all
internal parts were freely moving..

Predictably, this did not improve things. DHW will not fire up and neither
will the CH now.

The pump runs and you can hear water running round the system. Now I have
the covers off the boiler I can see that the Servo arm is moving ok when the
HW tap runs (so I guess the water section is ok) but the micro switches on
top of the diverter aren't moving at all. The push rod seems stuck in the
same half way position.
I can fire the CH with a screwdriver and I can fire the DHW by pulling the
micro switch out manually but in both cases the boiler cuts out after about
30 secs.
Also when I switch the CH off using the room thermostat control the pump
continues to run - although there is no demand. When I then cut it off using
the power switch the pump grinds to halt with what sounds ominously like a
death rattle.

It didn't do that before!!

I'm still going to change the DHW thermostat but I don't know if I should
change the diverter valve although it's not moving the micro switches I
couldn't see anything wrong with it when I stripped it down.
Could the pump have something to do with this?
Also I replaced the DHW expansion vessel about 18 months ago after a
failure. I've never been happy about it. Would an incorrectly pressured
vessel cause the diverter valve to stick?
Any suggestions would be gratefully received!

In message , Son of Fred
writes
Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose with
certainty.


Have you checked the diverter valve microswitches ?


--
geoff

I'm afraid the spindle/pushrod isn't moving the switches at all so I can't
adjust them.
I can fire the boiler by manually making the switches although it wont
remain lit.
The servo arm on top of the water section moves and returns OK.
I'm going to try venting the boiler this morning and if that fails cleaning
out the control lines this afternoon.

"geoff" wrote in message
...
In message , Son of Fred
writes
Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose with
certainty.


Have you checked the diverter valve microswitches ?


--
geoff

On Mon, 18 Aug 2008 23:08:30 +0100, Son of Fred wrote:

Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose
with certainty.

For some time we haven't been able to get the DHW to fire when we ran
the shower upstairs - if we opened another HW tap then it would. Some
time after we began to notice the water was getting v hot. Next thing
was that the pilot light would blow out when the water overheated. After
the pilot was relit the DHW would not easily fire again. We would have
to wait until the whole thing cooled down. During this time the CH
seemed to operate OK. Finally today, we could not get the DHW to fire at
all and something had to be done.

I thought the thermocouple was ok and the pilot problem was linked to
the overheating so I decided to replace the DHW thermostat and check and
replace the diaphragms in the 'water section' and the diverter valve -
(I had previously done this some years ago when we were getting no dhw
and I discovered a tear in one of the diaphragms.) Well, when I got home
from the Parts centre I found they had given me an NTC sensor not the
DHW thermostat - but I changed this anyway. I changed both the
diaphragms - although the old ones looked ok and all internal parts were
freely moving..

Predictably, this did not improve things. DHW will not fire up and
neither will the CH now.

The pump runs and you can hear water running round the system. Now I
have the covers off the boiler I can see that the Servo arm is moving ok
when the HW tap runs (so I guess the water section is ok) but the micro
switches on top of the diverter aren't moving at all. The push rod seems
stuck in the same half way position.
I can fire the CH with a screwdriver and I can fire the DHW by pulling
the micro switch out manually but in both cases the boiler cuts out
after about 30 secs.
Also when I switch the CH off using the room thermostat control the pump
continues to run - although there is no demand. When I then cut it off
using the power switch the pump grinds to halt with what sounds
ominously like a death rattle.

It didn't do that before!!

I'm still going to change the DHW thermostat but I don't know if I
should change the diverter valve although it's not moving the micro
switches I couldn't see anything wrong with it when I stripped it down.
Could the pump have something to do with this? Also I replaced the DHW
expansion vessel about 18 months ago after a failure. I've never been
happy about it. Would an incorrectly pressured vessel cause the diverter
valve to stick? Any suggestions would be gratefully received!

The pump noise does make me think this might be a pump problem.

All the symptoms from your description point to the pump. The microswitch
assy is porbably OK. I'm not sure but I think you can change the just the
pump head if so that will be fairly inexpensive to repair and try out.
If the pump was OK and you pushed the diverter to the left to get the CH
to start it should have continued to run OK.

This boiler is about 13-20 years old and should be possible to repair it
to give you quite a few more years.



--
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

In message , Son of Fred
writes
I'm afraid the spindle/pushrod isn't moving the switches at all so I can't
adjust them.
I can fire the boiler by manually making the switches although it wont
remain lit.
The servo arm on top of the water section moves and returns OK.
I'm going to try venting the boiler this morning and if that fails cleaning
out the control lines this afternoon.

you'll have to wait for Ed to appear, he's the hands on vaillant man

"geoff" wrote in message
...
In message , Son of Fred
writes
Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose with
certainty.


Have you checked the diverter valve microswitches ?


--
geoff



--
geoff

I thought I'd update my progress in case anyone might be able to shed any
light onto our problems.

First thing I did today was obtain and fit a new DHW thermostat along with
the new NTC probe in the hope if I could get the boiler working the DHW
would stop overheating.
I vented the boiler and bled the rads -- no effect

I then removed the main control line from the servo to the diverter. It was
well clogged up with crud. I cleaned it out refitted and Bingo! Boiler fired
up first time and stayed lit. I could get CH or DHW on demand. The pushrod
was moving freely and tripping the microswitches as required. I ran the DHW
for some time and the water temp stayed constant and the pilot remained lit
so at least the water temp issue is fixed however the upstairs shower still
would not fire the boiler. (The BAth and basin were OK). In view of the crud
down the control line I decided to strip the others out and clean them too.
Hey, It couldn't do any harm could it?
How I wish I had taken a shower first.
The other Control lines were cruddy too and I took the servo off and cleaned
the holes the lines went into best I could - these too were rather clogged.
When I refitted and tried to run the boiler to my surprise and frustration
we were back to square 1.No DHW or CH.
The situation is as per my first post i.e the servo arm rises and falls at
the right times but the diverter pushrod is not moving at all. I can fire
the boiler by making the switches manually but it will only run for 30 secs
before cutting out - even if I continue to make the switch.
If I pull out the spring loaded microswitch trip mech away from the diverter
while the H tap is running I can see the pushrod begin to move out but as
soon as I release it forces the rod backin. There is not enough pressure in
the diverter valve to hold it though the tap is running full pelt.
Although I had the boiler up and running earlier ther was one thing that
caught my eye. On one occasion while calling for dhw the pushrod was
extending out smoothly to the right hand side when all of a sudden it fell
back then shot out again like there had been a sudden dip in the pressure.
I'm stumped now. I'm thinking of replacing the servo and or diverter valve.
Does anyone else think this would be a good idea?
What should I try changing first?
I'm taking the kids round to me mums for showers now!

"Son of Fred" wrote in message
...
I'm afraid the spindle/pushrod isn't moving the switches at all so I
can't adjust them.
I can fire the boiler by manually making the switches although it wont
remain lit.
The servo arm on top of the water section moves and returns OK.
I'm going to try venting the boiler this morning and if that fails
cleaning out the control lines this afternoon.

"geoff" wrote in message
...
In message , Son of Fred
writes
Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose with
certainty.


Have you checked the diverter valve microswitches ?


--
geoff

Cheers Ed!!!
I got back from my ablutions at my old mum's and when I read your comments
re pushing the M/S assy all the way to left to fire
the CH I realised this is not what I've been doing.
I've been firing it by holding in the black switch with a screwdriver blade.
The boiler would fire for 30 secs then fade.
This made me realise the other microswitch needs to be depressed at the same
time.
As soon as I read your post I pushed in the M/S assy fully to the left as
you described and the boiler gave an almighty gurgle, fired and stayed lit.

The pushrod is moving freely once again and I can get CH and HW on demand.
Even the shower is firing the boiler now
(and that hasn't happened for a while now without opening up the basin HW
tap at the same time.)

I guess there must have got an airlock somewhere in the diverter (or the
pump?) after I refilled. Everything is running tickety boo now so
the I think key was cleaning out the control lines and the servo after all.

As you noted the pump dosen't sound too healthy. If I flip the mains power
switch when its running it comes to a halt with a clatter so maybe
thats going to be the next thing to go wrong. I was interested to learn from
your post I might not have to change the whole thing, and I'll keep that
in mind.

Many thanks to you and Geoff for the Input.

"Ed Sirett" wrote in message
...
On Mon, 18 Aug 2008 23:08:30 +0100, Son of Fred wrote:

Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose
with certainty.

For some time we haven't been able to get the DHW to fire when we ran
the shower upstairs - if we opened another HW tap then it would. Some
time after we began to notice the water was getting v hot. Next thing
was that the pilot light would blow out when the water overheated. After
the pilot was relit the DHW would not easily fire again. We would have
to wait until the whole thing cooled down. During this time the CH
seemed to operate OK. Finally today, we could not get the DHW to fire at
all and something had to be done.

I thought the thermocouple was ok and the pilot problem was linked to
the overheating so I decided to replace the DHW thermostat and check and
replace the diaphragms in the 'water section' and the diverter valve -
(I had previously done this some years ago when we were getting no dhw
and I discovered a tear in one of the diaphragms.) Well, when I got home
from the Parts centre I found they had given me an NTC sensor not the
DHW thermostat - but I changed this anyway. I changed both the
diaphragms - although the old ones looked ok and all internal parts were
freely moving..

Predictably, this did not improve things. DHW will not fire up and
neither will the CH now.

The pump runs and you can hear water running round the system. Now I
have the covers off the boiler I can see that the Servo arm is moving ok
when the HW tap runs (so I guess the water section is ok) but the micro
switches on top of the diverter aren't moving at all. The push rod seems
stuck in the same half way position.
I can fire the CH with a screwdriver and I can fire the DHW by pulling
the micro switch out manually but in both cases the boiler cuts out
after about 30 secs.
Also when I switch the CH off using the room thermostat control the pump
continues to run - although there is no demand. When I then cut it off
using the power switch the pump grinds to halt with what sounds
ominously like a death rattle.

It didn't do that before!!

I'm still going to change the DHW thermostat but I don't know if I
should change the diverter valve although it's not moving the micro
switches I couldn't see anything wrong with it when I stripped it down.
Could the pump have something to do with this? Also I replaced the DHW
expansion vessel about 18 months ago after a failure. I've never been
happy about it. Would an incorrectly pressured vessel cause the diverter
valve to stick? Any suggestions would be gratefully received!

The pump noise does make me think this might be a pump problem.

All the symptoms from your description point to the pump. The microswitch
assy is porbably OK. I'm not sure but I think you can change the just the
pump head if so that will be fairly inexpensive to repair and try out.
If the pump was OK and you pushed the diverter to the left to get the CH
to start it should have continued to run OK.

This boiler is about 13-20 years old and should be possible to repair it
to give you quite a few more years.



--
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

On Tue, 19 Aug 2008 23:37:30 +0100, Son of Fred wrote:

Cheers Ed!!!
I got back from my ablutions at my old mum's and when I read your
comments re pushing the M/S assy all the way to left to fire the CH I
realised this is not what I've been doing. I've been firing it by
holding in the black switch with a screwdriver blade. The boiler would
fire for 30 secs then fade. This made me realise the other microswitch
needs to be depressed at the same time.
As soon as I read your post I pushed in the M/S assy fully to the left
as you described and the boiler gave an almighty gurgle, fired and
stayed lit.

The pushrod is moving freely once again and I can get CH and HW on
demand. Even the shower is firing the boiler now (and that hasn't
happened for a while now without opening up the basin HW tap at the same
time.)

I guess there must have got an airlock somewhere in the diverter (or the
pump?) after I refilled. Everything is running tickety boo now so the I
think key was cleaning out the control lines and the servo after all.

As you noted the pump dosen't sound too healthy. If I flip the mains
power switch when its running it comes to a halt with a clatter so maybe
thats going to be the next thing to go wrong. I was interested to learn
from your post I might not have to change the whole thing, and I'll keep
that in mind.

Many thanks to you and Geoff for the Input.

"Ed Sirett" wrote in message
...
On Mon, 18 Aug 2008 23:08:30 +0100, Son of Fred wrote:

Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose
with certainty.

For some time we haven't been able to get the DHW to fire when we ran
the shower upstairs - if we opened another HW tap then it would. Some
time after we began to notice the water was getting v hot. Next thing
was that the pilot light would blow out when the water overheated.
After the pilot was relit the DHW would not easily fire again. We
would have to wait until the whole thing cooled down. During this time
the CH seemed to operate OK. Finally today, we could not get the DHW
to fire at all and something had to be done.

I thought the thermocouple was ok and the pilot problem was linked to
the overheating so I decided to replace the DHW thermostat and check
and replace the diaphragms in the 'water section' and the diverter
valve - (I had previously done this some years ago when we were
getting no dhw and I discovered a tear in one of the diaphragms.)
Well, when I got home from the Parts centre I found they had given me
an NTC sensor not the DHW thermostat - but I changed this anyway. I
changed both the diaphragms - although the old ones looked ok and all
internal parts were freely moving..

Predictably, this did not improve things. DHW will not fire up and
neither will the CH now.

The pump runs and you can hear water running round the system. Now I
have the covers off the boiler I can see that the Servo arm is moving
ok when the HW tap runs (so I guess the water section is ok) but the
micro switches on top of the diverter aren't moving at all. The push
rod seems stuck in the same half way position.
I can fire the CH with a screwdriver and I can fire the DHW by pulling
the micro switch out manually but in both cases the boiler cuts out
after about 30 secs.
Also when I switch the CH off using the room thermostat control the
pump continues to run - although there is no demand. When I then cut
it off using the power switch the pump grinds to halt with what sounds
ominously like a death rattle.

It didn't do that before!!

I'm still going to change the DHW thermostat but I don't know if I
should change the diverter valve although it's not moving the micro
switches I couldn't see anything wrong with it when I stripped it
down. Could the pump have something to do with this? Also I replaced
the DHW expansion vessel about 18 months ago after a failure. I've
never been happy about it. Would an incorrectly pressured vessel cause
the diverter valve to stick? Any suggestions would be gratefully
received!

The pump noise does make me think this might be a pump problem.

All the symptoms from your description point to the pump. The
microswitch assy is porbably OK. I'm not sure but I think you can
change the just the pump head if so that will be fairly inexpensive to
repair and try out. If the pump was OK and you pushed the diverter to
the left to get the CH to start it should have continued to run OK.

This boiler is about 13-20 years old and should be possible to repair
it to give you quite a few more years.


I did battle with the 18kW [1] version today. Having stripped the whole
of the domestic water switch unit down and found that it just needed a new
sindle gland...

So.. I was fully bracing my self for c. £100 (actually 75+VAT) for a new
'wasser schalter' but was well pleased to find that for £1.57 I could buy
a new 'stopfbuchse' (spindle gland) on its own.

Full marks to Vaillant and A10 boiler spares for making and stocking just
the part that needed replacing.


[1] designed for small flats with a shower but no bath.
--
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

In message , Ed Sirett
writes
On Tue, 19 Aug 2008 23:37:30 +0100, Son of Fred wrote:

Cheers Ed!!!
I got back from my ablutions at my old mum's and when I read your
comments re pushing the M/S assy all the way to left to fire the CH I
realised this is not what I've been doing. I've been firing it by
holding in the black switch with a screwdriver blade. The boiler would
fire for 30 secs then fade. This made me realise the other microswitch
needs to be depressed at the same time.
As soon as I read your post I pushed in the M/S assy fully to the left
as you described and the boiler gave an almighty gurgle, fired and
stayed lit.

The pushrod is moving freely once again and I can get CH and HW on
demand. Even the shower is firing the boiler now (and that hasn't
happened for a while now without opening up the basin HW tap at the same
time.)

I guess there must have got an airlock somewhere in the diverter (or the
pump?) after I refilled. Everything is running tickety boo now so the I
think key was cleaning out the control lines and the servo after all.

As you noted the pump dosen't sound too healthy. If I flip the mains
power switch when its running it comes to a halt with a clatter so maybe
thats going to be the next thing to go wrong. I was interested to learn
from your post I might not have to change the whole thing, and I'll keep
that in mind.

Many thanks to you and Geoff for the Input.

"Ed Sirett" wrote in message
...
On Mon, 18 Aug 2008 23:08:30 +0100, Son of Fred wrote:

Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose
with certainty.

For some time we haven't been able to get the DHW to fire when we ran
the shower upstairs - if we opened another HW tap then it would. Some
time after we began to notice the water was getting v hot. Next thing
was that the pilot light would blow out when the water overheated.
After the pilot was relit the DHW would not easily fire again. We
would have to wait until the whole thing cooled down. During this time
the CH seemed to operate OK. Finally today, we could not get the DHW
to fire at all and something had to be done.

I thought the thermocouple was ok and the pilot problem was linked to
the overheating so I decided to replace the DHW thermostat and check
and replace the diaphragms in the 'water section' and the diverter
valve - (I had previously done this some years ago when we were
getting no dhw and I discovered a tear in one of the diaphragms.)
Well, when I got home from the Parts centre I found they had given me
an NTC sensor not the DHW thermostat - but I changed this anyway. I
changed both the diaphragms - although the old ones looked ok and all
internal parts were freely moving..

Predictably, this did not improve things. DHW will not fire up and
neither will the CH now.

The pump runs and you can hear water running round the system. Now I
have the covers off the boiler I can see that the Servo arm is moving
ok when the HW tap runs (so I guess the water section is ok) but the
micro switches on top of the diverter aren't moving at all. The push
rod seems stuck in the same half way position.
I can fire the CH with a screwdriver and I can fire the DHW by pulling
the micro switch out manually but in both cases the boiler cuts out
after about 30 secs.
Also when I switch the CH off using the room thermostat control the
pump continues to run - although there is no demand. When I then cut
it off using the power switch the pump grinds to halt with what sounds
ominously like a death rattle.

It didn't do that before!!

I'm still going to change the DHW thermostat but I don't know if I
should change the diverter valve although it's not moving the micro
switches I couldn't see anything wrong with it when I stripped it
down. Could the pump have something to do with this? Also I replaced
the DHW expansion vessel about 18 months ago after a failure. I've
never been happy about it. Would an incorrectly pressured vessel cause
the diverter valve to stick? Any suggestions would be gratefully
received!

The pump noise does make me think this might be a pump problem.

All the symptoms from your description point to the pump. The
microswitch assy is porbably OK. I'm not sure but I think you can
change the just the pump head if so that will be fairly inexpensive to
repair and try out. If the pump was OK and you pushed the diverter to
the left to get the CH to start it should have continued to run OK.

This boiler is about 13-20 years old and should be possible to repair
it to give you quite a few more years.


I did battle with the 18kW [1] version today. Having stripped the whole
of the domestic water switch unit down and found that it just needed a new
sindle gland...

So.. I was fully bracing my self for c. £100 (actually 75+VAT) for a new
'wasser schalter' but was well pleased to find that for £1.57 I could buy
a new 'stopfbuchse' (spindle gland) on its own.

Full marks to Vaillant and A10 boiler spares for making and stocking just
the part that needed replacing.

A10 seem to have gone down hill a bit lately

Paul seems more concerned with fishing and holidays

shame really


--
geoff

On Thu, 21 Aug 2008 00:17:17 +0100, geoff wrote:

In message , Ed Sirett
writes
On Tue, 19 Aug 2008 23:37:30 +0100, Son of Fred wrote:

Cheers Ed!!!
I got back from my ablutions at my old mum's and when I read your
comments re pushing the M/S assy all the way to left to fire the CH I
realised this is not what I've been doing. I've been firing it by
holding in the black switch with a screwdriver blade. The boiler would
fire for 30 secs then fade. This made me realise the other microswitch
needs to be depressed at the same time. As soon as I read your post I
pushed in the M/S assy fully to the left as you described and the
boiler gave an almighty gurgle, fired and stayed lit.

The pushrod is moving freely once again and I can get CH and HW on
demand. Even the shower is firing the boiler now (and that hasn't
happened for a while now without opening up the basin HW tap at the
same time.)

I guess there must have got an airlock somewhere in the diverter (or
the pump?) after I refilled. Everything is running tickety boo now so
the I think key was cleaning out the control lines and the servo after
all.

As you noted the pump dosen't sound too healthy. If I flip the mains
power switch when its running it comes to a halt with a clatter so
maybe thats going to be the next thing to go wrong. I was interested
to learn from your post I might not have to change the whole thing,
and I'll keep that in mind.

Many thanks to you and Geoff for the Input.

"Ed Sirett" wrote in message
...
On Mon, 18 Aug 2008 23:08:30 +0100, Son of Fred wrote:

Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose
with certainty.

For some time we haven't been able to get the DHW to fire when we
ran the shower upstairs - if we opened another HW tap then it would.
Some time after we began to notice the water was getting v hot. Next
thing was that the pilot light would blow out when the water
overheated. After the pilot was relit the DHW would not easily fire
again. We would have to wait until the whole thing cooled down.
During this time the CH seemed to operate OK. Finally today, we
could not get the DHW to fire at all and something had to be done.

I thought the thermocouple was ok and the pilot problem was linked
to the overheating so I decided to replace the DHW thermostat and
check and replace the diaphragms in the 'water section' and the
diverter valve - (I had previously done this some years ago when we
were getting no dhw and I discovered a tear in one of the
diaphragms.) Well, when I got home from the Parts centre I found
they had given me an NTC sensor not the DHW thermostat - but I
changed this anyway. I changed both the diaphragms - although the
old ones looked ok and all internal parts were freely moving..

Predictably, this did not improve things. DHW will not fire up and
neither will the CH now.

The pump runs and you can hear water running round the system. Now I
have the covers off the boiler I can see that the Servo arm is
moving ok when the HW tap runs (so I guess the water section is ok)
but the micro switches on top of the diverter aren't moving at all.
The push rod seems stuck in the same half way position. I can fire
the CH with a screwdriver and I can fire the DHW by pulling the
micro switch out manually but in both cases the boiler cuts out
after about 30 secs.
Also when I switch the CH off using the room thermostat control the
pump continues to run - although there is no demand. When I then cut
it off using the power switch the pump grinds to halt with what
sounds ominously like a death rattle.

It didn't do that before!!

I'm still going to change the DHW thermostat but I don't know if I
should change the diverter valve although it's not moving the micro
switches I couldn't see anything wrong with it when I stripped it
down. Could the pump have something to do with this? Also I replaced
the DHW expansion vessel about 18 months ago after a failure. I've
never been happy about it. Would an incorrectly pressured vessel
cause the diverter valve to stick? Any suggestions would be
gratefully received!

The pump noise does make me think this might be a pump problem.

All the symptoms from your description point to the pump. The
microswitch assy is porbably OK. I'm not sure but I think you can
change the just the pump head if so that will be fairly inexpensive
to repair and try out. If the pump was OK and you pushed the diverter
to the left to get the CH to start it should have continued to run
OK.

This boiler is about 13-20 years old and should be possible to repair
it to give you quite a few more years.


I did battle with the 18kW [1] version today. Having stripped the whole
of the domestic water switch unit down and found that it just needed a
new sindle gland...

So.. I was fully bracing my self for c. £100 (actually 75+VAT) for a new
'wasser schalter' but was well pleased to find that for £1.57 I could
buy a new 'stopfbuchse' (spindle gland) on its own.

Full marks to Vaillant and A10 boiler spares for making and stocking
just the part that needed replacing.

A10 seem to have gone down hill a bit lately

Paul seems more concerned with fishing and holidays

shame really

They seem to be helping me OK. I haven't seem the guy with the glasses
around lately? Is he Paul?
He is legendary: he spots the broken part as you walk along the street
from your van and gets it from the store room ready for when you walk in.

--
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

In message , Ed Sirett
writes
Full marks to Vaillant and A10 boiler spares for making and stocking
just the part that needed replacing.

A10 seem to have gone down hill a bit lately

Paul seems more concerned with fishing and holidays

shame really

They seem to be helping me OK. I haven't seem the guy with the glasses
around lately?

Kevin - poached from FMT

Is he Paul?

Paul is tall and a bit fat (who am I to talk ??)

He is legendary: he spots the broken part as you walk along the street
from your van and gets it from the store room ready for when you walk in.


--
geoff

I think I have celebrated too soon as I still have one of my original
problems. That is the pilot is still blowing out AFTER I have run DHW for
some time.
About 20 seconds after the HW is turned off after a long run (Bath fill or
long shower session) then I hear the thermocouple shut off the pilot.

So far I have replaced the DHW thermostat and the NTC probe thinking this
was linked.
There is a DHW flow regulator on the water section but this has been seized
up in the same position for the last 15 years!
I had to replace the thermocouple 2 years ago as it was failing - but it was
behaving v erractically - dropping out v frequently in CH, DHW or idle modes
so I dont think it's the thermocouple- but I could be wrong.
Is there anything else it could be?
Otherwise I will have to replace the thermocouple for elimination purposes.


"geoff" wrote in message
...
In message , Ed Sirett
writes
On Tue, 19 Aug 2008 23:37:30 +0100, Son of Fred wrote:

Cheers Ed!!!
I got back from my ablutions at my old mum's and when I read your
comments re pushing the M/S assy all the way to left to fire the CH I
realised this is not what I've been doing. I've been firing it by
holding in the black switch with a screwdriver blade. The boiler would
fire for 30 secs then fade. This made me realise the other microswitch
needs to be depressed at the same time.
As soon as I read your post I pushed in the M/S assy fully to the left
as you described and the boiler gave an almighty gurgle, fired and
stayed lit.

The pushrod is moving freely once again and I can get CH and HW on
demand. Even the shower is firing the boiler now (and that hasn't
happened for a while now without opening up the basin HW tap at the same
time.)

I guess there must have got an airlock somewhere in the diverter (or the
pump?) after I refilled. Everything is running tickety boo now so the I
think key was cleaning out the control lines and the servo after all.

As you noted the pump dosen't sound too healthy. If I flip the mains
power switch when its running it comes to a halt with a clatter so maybe
thats going to be the next thing to go wrong. I was interested to learn
from your post I might not have to change the whole thing, and I'll keep
that in mind.

Many thanks to you and Geoff for the Input.

"Ed Sirett" wrote in message
...
On Mon, 18 Aug 2008 23:08:30 +0100, Son of Fred wrote:

Our ancient Vaillant combi (VCW GB240H ) will no longer fire. The
culmination of a series of problems I found to difficult to diagnose
with certainty.

For some time we haven't been able to get the DHW to fire when we ran
the shower upstairs - if we opened another HW tap then it would. Some
time after we began to notice the water was getting v hot. Next thing
was that the pilot light would blow out when the water overheated.
After the pilot was relit the DHW would not easily fire again. We
would have to wait until the whole thing cooled down. During this time
the CH seemed to operate OK. Finally today, we could not get the DHW
to fire at all and something had to be done.

I thought the thermocouple was ok and the pilot problem was linked to
the overheating so I decided to replace the DHW thermostat and check
and replace the diaphragms in the 'water section' and the diverter
valve - (I had previously done this some years ago when we were
getting no dhw and I discovered a tear in one of the diaphragms.)
Well, when I got home from the Parts centre I found they had given me
an NTC sensor not the DHW thermostat - but I changed this anyway. I
changed both the diaphragms - although the old ones looked ok and all
internal parts were freely moving..

Predictably, this did not improve things. DHW will not fire up and
neither will the CH now.

The pump runs and you can hear water running round the system. Now I
have the covers off the boiler I can see that the Servo arm is moving
ok when the HW tap runs (so I guess the water section is ok) but the
micro switches on top of the diverter aren't moving at all. The push
rod seems stuck in the same half way position.
I can fire the CH with a screwdriver and I can fire the DHW by pulling
the micro switch out manually but in both cases the boiler cuts out
after about 30 secs.
Also when I switch the CH off using the room thermostat control the
pump continues to run - although there is no demand. When I then cut
it off using the power switch the pump grinds to halt with what sounds
ominously like a death rattle.

It didn't do that before!!

I'm still going to change the DHW thermostat but I don't know if I
should change the diverter valve although it's not moving the micro
switches I couldn't see anything wrong with it when I stripped it
down. Could the pump have something to do with this? Also I replaced
the DHW expansion vessel about 18 months ago after a failure. I've
never been happy about it. Would an incorrectly pressured vessel cause
the diverter valve to stick? Any suggestions would be gratefully
received!

The pump noise does make me think this might be a pump problem.

All the symptoms from your description point to the pump. The
microswitch assy is porbably OK. I'm not sure but I think you can
change the just the pump head if so that will be fairly inexpensive to
repair and try out. If the pump was OK and you pushed the diverter to
the left to get the CH to start it should have continued to run OK.

This boiler is about 13-20 years old and should be possible to repair
it to give you quite a few more years.


I did battle with the 18kW [1] version today. Having stripped the whole
of the domestic water switch unit down and found that it just needed a new
sindle gland...

So.. I was fully bracing my self for c. £100 (actually 75+VAT) for a new
'wasser schalter' but was well pleased to find that for £1.57 I could buy
a new 'stopfbuchse' (spindle gland) on its own.

Full marks to Vaillant and A10 boiler spares for making and stocking just
the part that needed replacing.

A10 seem to have gone down hill a bit lately

Paul seems more concerned with fishing and holidays

shame really


--
geoff