We have a Vaillant Ecomax 835/2E, which was recommended and fitted in
2003 by our neighbour who runs his own gas fitting business and who
does our servicing of it.
Recently the boiler developed a problem with hot water delivery. The
water ran very hot for about 30 seconds then slowly cooled over the
next 2 minutes until luke warm. We found that by turning the tap on
very low, thereby reducing the flow of water it was possible to run a
bath in about 20 minutes.
We asked our gas fitter neighbour to carry out a repair for us.
He replaced the diverter valve and NTC sensor. Removed the heat
exchanger and flushed it through with a machine and a cleaning
solution.
We also decided that it would not hurt to add a Magnaclean appliance
to the system to help remove the accumulation of black sludge that
forms there. This was fitted and a bottle of SM3 system cleaner was
added and ran for 2 weeks before flushing and refilling.
All of this has made no difference and we still have the exact same
problem.
Our fitter phoned Vaillant several times for technical advice and they
advised changing the heat exchanger but because the actual flow of
water is very good with the tap full on the heat exchanger does not
appear to be blocked.
We are now in an embarrassing situation with our neighbour and friend,
in that we have spent a fair amount of money on a repair that has, so
far, been unsuccessful and are scared to replace the heat exchanger,
when it seems by no means certain that it will solve the problem.

With the hot water thermostat set at half way and the tap full on
Boiler reads 71 C after 25 seconds
Then starts to drop 47 C after next 30 seconds
39 C after next 30 seconds
35 C after next 30 seconds
34 C after next 30 seconds
Remaining at 34 C thereafter.


I would be most grateful for any advice you may be able to give.

On Mon, 16 Feb 2009 14:55:55 -0800, Ron wrote:

I would be most grateful for any advice you may be able to give.

Are you in a hard water area?
If so, what sort of scale inhibitor does the system require (see the
installation manual) and what type does it have?


--
John Stumbles -- http://yaph.co.uk

Death is nature's way of telling you to slow down

In message
, Ron
writes
We have a Vaillant Ecomax 835/2E, which was recommended and fitted in
2003 by our neighbour who runs his own gas fitting business and who
does our servicing of it.

filling

I would be most grateful for any advice you may be able to give.

I would rarely point people to the diynot forum, as it's populated by a
load of sad fitters with no life

http://www.diynot.com/forums/

However, in this case, I think that you might find someone there who
might have an answer

don't forget to point out that a CORGI fitter is doing the work, they
can be a bit sensitive

--
geoff

Ron wrote:
We have a Vaillant Ecomax 835/2E, which was recommended and fitted in
2003 by our neighbour who runs his own gas fitting business and who
does our servicing of it.
Recently the boiler developed a problem with hot water delivery. The
water ran very hot for about 30 seconds then slowly cooled over the
next 2 minutes until luke warm. We found that by turning the tap on
very low, thereby reducing the flow of water it was possible to run a
bath in about 20 minutes.
We asked our gas fitter neighbour to carry out a repair for us.
He replaced the diverter valve and NTC sensor. Removed the heat
exchanger and flushed it through with a machine and a cleaning
solution.
We also decided that it would not hurt to add a Magnaclean appliance
to the system to help remove the accumulation of black sludge that
forms there. This was fitted and a bottle of SM3 system cleaner was
added and ran for 2 weeks before flushing and refilling.
All of this has made no difference and we still have the exact same
problem.
Our fitter phoned Vaillant several times for technical advice and they
advised changing the heat exchanger but because the actual flow of
water is very good with the tap full on the heat exchanger does not
appear to be blocked.
We are now in an embarrassing situation with our neighbour and friend,
in that we have spent a fair amount of money on a repair that has, so
far, been unsuccessful and are scared to replace the heat exchanger,
when it seems by no means certain that it will solve the problem.

With the hot water thermostat set at half way and the tap full on
Boiler reads 71 C after 25 seconds
Then starts to drop 47 C after next 30 seconds
39 C after next 30 seconds
35 C after next 30 seconds
34 C after next 30 seconds
Remaining at 34 C thereafter.


I would be most grateful for any advice you may be able to give.

This is why I prefer the insurance option. They can replace things on a
trial and error basis at their expense rather than mine.

Ron wrote:

Recently the boiler developed a problem with hot water delivery. The
water ran very hot for about 30 seconds then slowly cooled over the
next 2 minutes until luke warm. We found that by turning the tap on
very low, thereby reducing the flow of water it was possible to run a
bath in about 20 minutes.
We asked our gas fitter neighbour to carry out a repair for us.
He replaced the diverter valve and NTC sensor. Removed the heat
exchanger and flushed it through with a machine and a cleaning
solution.
We also decided that it would not hurt to add a Magnaclean appliance
to the system to help remove the accumulation of black sludge that
forms there. This was fitted and a bottle of SM3 system cleaner was
added and ran for 2 weeks before flushing and refilling.
All of this has made no difference and we still have the exact same
problem.

As all of what you have done appears to be for the primary heating side I am
not surprised it had no effect on the hot water.

Our fitter phoned Vaillant several times for technical advice and they
advised changing the heat exchanger but because the actual flow of
water is very good with the tap full on the heat exchanger does not
appear to be blocked.

Is this the problem?
Is the flow of water too high?
Combis usually have some sort of flow limiter to ensure that there isn't too
much water going through them.
If there is they can't heat it fast enough.
Is the flow faster than it used to be?
Does it start of slow (and hot) and then increase (and cool)?
Has anyone checked the flow limiter is still working?

Time how long it takes to output 5-10 liters and post the results here and
someone can work out if it is just too much.

We are now in an embarrassing situation with our neighbour and friend,
in that we have spent a fair amount of money on a repair that has, so
far, been unsuccessful and are scared to replace the heat exchanger,
when it seems by no means certain that it will solve the problem.

I would do a few flow checks first.

Thanks for the input.

We are in a hard water area SE London. The water goes through a water
softener (Permutit Ecowater) So I would hope that would deal with
water hardness.
I ran 10litres of hot water with the tap full on from a standard
kitchen tap in 56 seconds.
If the tap is only turned on a little, as the water starts to heat it
will slow to about half the rate or even stop. I think this could be
some sort of safety thing. If I turn the tap on 'just enough' it will
run hot all the time but will take 20 minutes to run a bath.

On Mon, 16 Feb 2009 14:55:55 -0800, Ron wrote:

We have a Vaillant Ecomax 835/2E, which was recommended and fitted in
2003 by our neighbour who runs his own gas fitting business and who does
our servicing of it.
Recently the boiler developed a problem with hot water delivery. The
water ran very hot for about 30 seconds then slowly cooled over the next
2 minutes until luke warm. We found that by turning the tap on very low,
thereby reducing the flow of water it was possible to run a bath in
about 20 minutes.
We asked our gas fitter neighbour to carry out a repair for us. He
replaced the diverter valve and NTC sensor. Removed the heat exchanger
and flushed it through with a machine and a cleaning solution.
We also decided that it would not hurt to add a Magnaclean appliance to
the system to help remove the accumulation of black sludge that forms
there. This was fitted and a bottle of SM3 system cleaner was added and
ran for 2 weeks before flushing and refilling. All of this has made no
difference and we still have the exact same problem.
Our fitter phoned Vaillant several times for technical advice and they
advised changing the heat exchanger but because the actual flow of water
is very good with the tap full on the heat exchanger does not appear to
be blocked.
We are now in an embarrassing situation with our neighbour and friend,
in that we have spent a fair amount of money on a repair that has, so
far, been unsuccessful and are scared to replace the heat exchanger,
when it seems by no means certain that it will solve the problem.

With the hot water thermostat set at half way and the tap full on Boiler
reads 71 C after 25 seconds
Then starts to drop 47 C after next 30 seconds
39 C after next 30 seconds
35 C after next 30 seconds
34 C after next 30 seconds
Remaining at 34 C thereafter.


I would be most grateful for any advice you may be able to give.

What is the actual flow rate of water you are getting out of the hot tap?
What speed is the combustion fan working at during HW production this is
on parameter d.33 or d.34 (if they are different to each other then that
is also significant).

The NTC would be the obvious thing to change but that's been done.
What effect does moving the max HW temp dial when doing HW?


--
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 17 Feb, 00:39, geoff wrote:
In message
, Ron
writes

We have a Vaillant Ecomax 835/2E, which was recommended and fitted in
2003 by our neighbour who runs his own gas fitting business and who
does our servicing of it.

filling

I would be most grateful for any advice you may be able to give.

I would rarely point people to the diynot forum, as it's populated by a
load of sad fitters with no life

http://www.diynot.com/forums/

However, in this case, I think that you might find someone there who
might have an answer

don't forget to point out that a CORGI fitter is doing the work, they
can be a bit sensitive

--
geoff

I have a diynot account, I can post this on behalf of the OP if he
wishes.

There are a few Vaillant approved engineers on there apparently

In message
,
David writes
On 17 Feb, 00:39, geoff wrote:
In message
, Ron
writes

We have a Vaillant Ecomax 835/2E, which was recommended and fitted in
2003 by our neighbour who runs his own gas fitting business and who
does our servicing of it.

filling

I would be most grateful for any advice you may be able to give.

I would rarely point people to the diynot forum, as it's populated by a
load of sad fitters with no life

http://www.diynot.com/forums/

However, in this case, I think that you might find someone there who
might have an answer

don't forget to point out that a CORGI fitter is doing the work, they
can be a bit sensitive

--
geoff

I have a diynot account, I can post this on behalf of the OP if he
wishes.

could do, but, there's nothing to stop him signing up


There are a few Vaillant approved engineers on there apparently

.... fitters - please

they don't and are not allowed to, engineer anything


--
geoff