Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

This points to a blockage in the DHW heat exchanger. Flushed it out.
Still the same. Fitted new DHW heat exchanger. Improved things for a
week or so.

Went back to its old stop/start routine. So filled up with cleaning
fluid (Fernox iirc) left in for a week, flushed through etc, made little
difference, and the exiting water didnt seem particulalry dirty.
So, last gasp attempt, filled with more cleaning fluid, left in for 2
weeks, flushed through thoroughly.
This also made no difference.
DHW H/E off again - clear, no blockage.

This now points to a primary heat exchanger blockage.
To try to discount other possiblilties, I have cleaned the flue, the
diverter valve insides, and other accessible parts.
Still playing up.

A new primary H/E is around £300 iirc. Half the price of a new boiler,
and it looks like it will be a swine to fit, as all the joints are
seized.

So, have I missed anything before I scrap this one?
Thanks
Alan.

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In article ,
(A.Lee) writes:
Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

This points to a blockage in the DHW heat exchanger. Flushed it out.

It doesn't. If it was that, it would only happen when combi
fires up for DHW, but you indicate it happens with CH too.

Still the same. Fitted new DHW heat exchanger. Improved things for a
week or so.

Went back to its old stop/start routine. So filled up with cleaning
fluid (Fernox iirc) left in for a week, flushed through etc, made little
difference, and the exiting water didnt seem particulalry dirty.
So, last gasp attempt, filled with more cleaning fluid, left in for 2
weeks, flushed through thoroughly.
This also made no difference.
DHW H/E off again - clear, no blockage.

This now points to a primary heat exchanger blockage.
To try to discount other possiblilties, I have cleaned the flue, the
diverter valve insides, and other accessible parts.
Still playing up.

A new primary H/E is around £300 iirc. Half the price of a new boiler,
and it looks like it will be a swine to fit, as all the joints are
seized.

So, have I missed anything before I scrap this one?

Most likely, it means the system can't get the heat out past some
point in the system, and the part before that overheats. You need
to trace how far the heat is getting through the system to find
the point where it gets no further, and identify the point where
the fault is. One possibility that spings to mind is the pump.
A friend had one which somehow lost most of its impellers and
resulted in very sluggish flow.

The other possibility is that nothing is overheating but a sensor
has gone bad. Does it look or sound like the system is overheating
when it goes off?

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Sat, 18 Oct 2008 12:47:27 +0100, A.Lee wrote:

Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

Is the pump working properly?

If not it won't shift hot water away from the heat exchanger fast enough.

In CH mode when the boiler runs (starting from cold is easier to tell) you
should get the flow pipe getting almost evenly hot for a good distance
(further along the longer it runs). If it's localised suggests the pump's
not working well.



--
YAPH http://yaph.co.uk

A: Because it messes up the order in which people read text.
Q: Why is top-posting a bad thing?

On Sat, 18 Oct 2008 12:47:27 +0100, A.Lee wrote:

Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

This points to a blockage in the DHW heat exchanger. Flushed it out.
Still the same. Fitted new DHW heat exchanger. Improved things for a
week or so.

Went back to its old stop/start routine. So filled up with cleaning
fluid (Fernox iirc) left in for a week, flushed through etc, made little
difference, and the exiting water didnt seem particulalry dirty.
So, last gasp attempt, filled with more cleaning fluid, left in for 2
weeks, flushed through thoroughly.
This also made no difference.
DHW H/E off again - clear, no blockage.

This now points to a primary heat exchanger blockage.
To try to discount other possiblilties, I have cleaned the flue, the
diverter valve insides, and other accessible parts.
Still playing up.

A new primary H/E is around £300 iirc. Half the price of a new boiler,
and it looks like it will be a swine to fit, as all the joints are
seized.

So, have I missed anything before I scrap this one?
Thanks
Alan.

=========================================
On one occasion recently I found a large accumulation of debris almost
blocking the pipe immediately before the pump. Cleaning and flushing had
obviously not shifted it. It might be worth removing your pump and valves
to see if a trap has been created there similar to mine.

Cic.

--
==========================================
Using Ubuntu Linux
Windows shown the door
==========================================

"Andrew Gabriel" wrote in message
...

One possibility that spings to mind is the pump.
A friend had one which somehow lost most of its impellers and
resulted in very sluggish flow.

Cavitation does that to impellers.
I had one go on mine once when I fitted a pump that needed a higher static
head than I had.
Serves me right for buying a special offer without reading the spec.

Andrew Gabriel wrote:

In article ,
(A.Lee) writes:
Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

This points to a blockage in the DHW heat exchanger. Flushed it out.

It doesn't. If it was that, it would only happen when combi
fires up for DHW, but you indicate it happens with CH too.

The CH cutting out didnt happen until quite recently, I had a
'qualified' CORGI man come round when it first started doing it, he
immediately said DHW exchanger, then said I could DIY as it was so easy.
It did sure it for 6 months, but then started to get worse.

Still the same. Fitted new DHW heat exchanger. Improved things for a
week or so.
....
So, have I missed anything before I scrap this one?

Most likely, it means the system can't get the heat out past some
point in the system, .... One possibility that spings to mind is the pump.
A friend had one which somehow lost most of its impellers and
resulted in very sluggish flow.

The pump may well be the cause. I took it off, and it looked in not too
bad condition, but it is pretty difficult to test its flow rate, so I
bit the bullet, and went down to Screwfix to buy a new one, but, as the
one I have has non-std. 1 1/4" outlets, they didnt have any, called into
B+Q, they only had 2". Bugger.
So put back the old one, and checked the attached air siphon, which was
blocked up - this may well have been a cause, as if air was in there,
when the pump was going round, it would be compressing the air, as well
as trying to pump water, hence the efficiency of the pump would be
lowered. Tested it once before posting this, and it has improved
matters, though it still cuts out after 30 seconds or so, which is a
good improvement, though obviously not cured.
Is there any way of testing pump flow rate apart from fitting a new
pump?

The other possibility is that nothing is overheating but a sensor
has gone bad. Does it look or sound like the system is overheating
when it goes off?

Both sensors were replaced a couple of months back, before the DHW H/E
was replaced, I had already been onto Alpha to ask their opinion, they
told me sensors first, good flush etc, then new H/E's.
Thanks
Alan.
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To reply by e-mail, change the ' + ' to 'plus'.

YAPH wrote:

On Sat, 18 Oct 2008 12:47:27 +0100, A.Lee wrote:

Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

Is the pump working properly?

If not it won't shift hot water away from the heat exchanger fast enough.

Possibly, see other post, though, apart from fitting a new pump, how can
the flow rate be checked?
Thanks
Alan.
--
To reply by e-mail, change the ' + ' to 'plus'.

Cicero wrote:

On Sat, 18 Oct 2008 12:47:27 +0100, A.Lee wrote:

Before I bite the bullet, and get a new boiler, maybe someone could
suggest something that I havent done to try to repair this one.
DHW (and CH) comes on for 20 seconds, cuts out, comes on after 10-20
secs, then repeats.

On one occasion recently I found a large accumulation of debris almost
blocking the pipe immediately before the pump. Cleaning and flushing had
obviously not shifted it. It might be worth removing your pump and valves
to see if a trap has been created there similar to mine.

No grunge build up anywhere that I have seen. The pump innards were
quite clean.
Thanks
Alan.
--
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