I've been having problems with my hot water for nearly a year now, where
the boiler burners would turn off for 30 seconds or so when the hot
water was on.
I had a CORGI man round to have a look, he seemed to think it was the
DHW heat exchanger blocked up, he said I was quite capable of doing it
myself, so I took it apart, flushed it through, and it was fine for 6
months or so.
It was cleaned again a month or so ago, but it didnt cure it this
time,just made it a little bit better, in that the hot water would run
for 5 minutes before cutting out, rather than the previous 2 minutes.

I have since put in cleaning fluid to the primary side via one of the
radiators, and ran them on and off for the last 3 weeks with this
cleaning fluid in. I flushed them through yesterday, though there didnt
appear to be any sludge in the system at all.

This made no difference to the DHW.

What is the next step?
A new DHW exchanger is £70ish - maybe get one, or could the old one be
brought back to life by soaking it in cleaning fluid.

If a new exchanger is the best solution, then I would rather do that
than spend more time trying to fix the old one.
If not the exchanger, what else should be checked?
BTW, the CH works fine.

Ta
Alan.

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I've been having problems with my hot water for nearly a year now, where
the boiler burners would turn off for 30 seconds or so when the hot
water was on.

And of course, I left out the important bit that this is on an Alpha
Combi boiler that is around 10 years old.
Alan.
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On Mon, 28 Jul 2008 21:33:09 +0100, A.Lee wrote:

I've been having problems with my hot water for nearly a year now, where
the boiler burners would turn off for 30 seconds or so when the hot
water was on.
I had a CORGI man round to have a look, he seemed to think it was the
DHW heat exchanger blocked up, he said I was quite capable of doing it
myself, so I took it apart, flushed it through, and it was fine for 6
months or so.
It was cleaned again a month or so ago, but it didnt cure it this
time,just made it a little bit better, in that the hot water would run
for 5 minutes before cutting out, rather than the previous 2 minutes.

I have since put in cleaning fluid to the primary side via one of the
radiators, and ran them on and off for the last 3 weeks with this
cleaning fluid in. I flushed them through yesterday, though there didnt
appear to be any sludge in the system at all.

This made no difference to the DHW.

What is the next step?
A new DHW exchanger is £70ish - maybe get one, or could the old one be
brought back to life by soaking it in cleaning fluid.

If a new exchanger is the best solution, then I would rather do that
than spend more time trying to fix the old one. If not the exchanger,
what else should be checked? BTW, the CH works fine.

Ta
Alan.


What are you cleaning it out with?
If dilute HCl then you shoudl get a result or a leak 8-(.

Buy replacement unit. Put existing unit in Dilute HCl (e.g. Screwfix
Patio Cleaner) and leave for a couple of days.

You then have a spare.


--
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 article ,
Ed Sirett writes:

What are you cleaning it out with?
If dilute HCl then you shoudl get a result or a leak 8-(.

Buy replacement unit. Put existing unit in Dilute HCl (e.g. Screwfix
Patio Cleaner) and leave for a couple of days.

You then have a spare.

It's easy enough to clean with Furnox DS3 (sulphamic acid with
an indicator dye so you know when it's exhausted). I stood the
plate exchanger in a washing up bowl and poured a jug of hot
dissolved DS3 in one end. Fizzes like mad. Bowl allows you to
collect it and pour it through again. When it changes from
yellow to green, you need to chuck it and mix up a fresh lot.
Keep doing this until it's stopped fizzing and won't go green
(i.e. no scale left). Probably took me about 20 minutes for a
Baxi one. Watch out for the fine acid spray from the fizz going
up your nose - not very pleasent. Also the indicator dye stains
some things (washing up brush had green or yellow bristles from
then on, depending if you dunked it in something acid or alkali:-).

If it's the primary side which is blocked, then sulphamic acid
probably won't clear that. That tends to block with rust
particles, not scale. If that's the case, some tell-tale ones
would like be dislodged by running water through it and tapping
it.

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

In message , A.Lee
writes
I've been having problems with my hot water for nearly a year now, where
the boiler burners would turn off for 30 seconds or so when the hot
water was on.
I had a CORGI man round to have a look, he seemed to think it was the
DHW heat exchanger blocked up, he said I was quite capable of doing it
myself, so I took it apart, flushed it through, and it was fine for 6
months or so.

Yes, but did you descale it properly ?

How did you flush it

It was cleaned again a month or so ago, but it didnt cure it this
time,just made it a little bit better, in that the hot water would run
for 5 minutes before cutting out, rather than the previous 2 minutes.

I have since put in cleaning fluid to the primary side via one of the
radiators, and ran them on and off for the last 3 weeks with this
cleaning fluid in. I flushed them through yesterday, though there didnt
appear to be any sludge in the system at all.

This made no difference to the DHW.

well, it wouldn't, would it ?


What is the next step?

descale it properly?


A new DHW exchanger is £70ish - maybe get one, or could the old one be
brought back to life by soaking it in cleaning fluid.

If a new exchanger is the best solution, then I would rather do that
than spend more time trying to fix the old one.
If not the exchanger, what else should be checked?
BTW, the CH works fine.

Ta
Alan.


--
geoff

On 28 Jul, 22:34, (Andrew Gabriel) wrote:

It's easy enough to clean with Furnox DS3 (sulphamic acid with
an indicator dye so you know when it's exhausted). I stood the
plate exchanger in a washing up bowl and poured a jug of hot
dissolved DS3 in one end. Fizzes like mad. Bowl allows you to
collect it and pour it through again. When it changes from
yellow to green, you need to chuck it and mix up a fresh lot.
Keep doing this until it's stopped fizzing and won't go green
(i.e. no scale left). Probably took me about 20 minutes for a
Baxi one. Watch out for the fine acid spray from the fizz going
up your nose - not very pleasent. Also the indicator dye stains
some things (washing up brush had green or yellow bristles from
then on, depending if you dunked it in something acid or alkali:-).

If it's the primary side which is blocked, then sulphamic acid
probably won't clear that. That tends to block with rust
particles, not scale. If that's the case, some tell-tale ones
would like be dislodged by running water through it and tapping
it.

When I had similar problems I found that the primary side was clogged
up with black flakes which I assumed were magnetite - iron I oxide I
seem to remember from school, as opposed to red rust which is iron III
oxide. Magnetite is much more or a pain in the arse than limescale on
the secondary side, which as Andrew says is easily cleared by a bit of
DS3.

I've asked in here before whether there is any straightforward
chemical process for dissolving iron I oxide, but the general opinion
seems to be "no". (Further vague schoolboy memories suggest some sort
of reduction reaction would be necessary?).

Anyway, in my case I did manage to restore the heat exchanger to
working order by blasting a lot of mains-pressure water through the
primary side and bashing it about quite a bit to loosen the crud. It's
got a few dents now as the scars of battle, but it works like a
good'un. If only that worked for all of life's little problems.

Cheers!

Martin

geoff wrote:

In message , A.Lee
writes
I've been having problems with my hot water ....
I had a CORGI man round to have a look, he seemed to think it was the
DHW heat exchanger blocked up, ...so I took it apart, flushed it through,

Yes, but did you descale it properly ?

Obviously not.

How did you flush it

Hosepipe in one hole, water comes out other.Repeat for other holes.

I have since put in cleaning fluid to the primary side via one of the
radiators, and ran them on and off for the last 3 weeks with this
cleaning fluid in. I flushed them through yesterday, though there didnt
appear to be any sludge in the system at all.

This made no difference to the DHW.

well, it wouldn't, would it ?

But the primary water does go round the DHW exchanger doesnt it, so the
cleaning fluid, I thought, would help to clean it out.

What is the next step?

descale it properly?

Easier said than done.You cannot see in there apart from the first
inch.If there is a rust blockage, it is not visible.When I cleared it a
few weeks ago, nothing at all came out, apart from clear water - I was
spraying into a large bucket so would see any flakes.
I'll be ordering a new one now anyway, as I'm getting annoyed with it.
Ta
Alan.


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To reply by e-mail, change the ' + ' to 'plus'.

In message , A.Lee
writes
geoff wrote:

In message , A.Lee
writes
I've been having problems with my hot water ....
I had a CORGI man round to have a look, he seemed to think it was the
DHW heat exchanger blocked up, ...so I took it apart, flushed it through,

Yes, but did you descale it properly ?

Obviously not.

How did you flush it

Hosepipe in one hole, water comes out other.Repeat for other holes.

you need some way of keeping a flow going or else you get dead spots of
"neutral" with no acid left to remove it


I have since put in cleaning fluid to the primary side via one of the
radiators, and ran them on and off for the last 3 weeks with this
cleaning fluid in. I flushed them through yesterday, though there didnt
appear to be any sludge in the system at all.

This made no difference to the DHW.

well, it wouldn't, would it ?

But the primary water does go round the DHW exchanger doesnt it, so the
cleaning fluid, I thought, would help to clean it out.

through the other side of the exchanger.

What is the next step?

descale it properly?

Easier said than done.You cannot see in there apart from the first
inch.

Yeah, without some means of circulation, it's difficult to do it
properly

--
geoff