Boiler gone again

[tjw1701]

Hi,

Firstly appologies if this ends up a little long!

I have a Worcester Bosh 24ri boiler which is connected to an Albion 210litre direct thermal store. They were both fitted around 5 years ago, and today I had to have my second heat exchanger fitted to the boiler, so I am getting through them at a rate of 1 every 2 and a half years.....pricey.

My concern is, in another 2.5 years I will be in the same place again so am really looking for any advice on where I could look to find the problem. Here is some background.

About half of the pipework is original (could be anything up to 30-40 years old) the rest has been fitted within the last 5 years. Most of the radiators are also 5 years or less old. The thermal store is also 5 years old and the whole lot has 12 litres of fernox MB1 in it as inhibitor.

The first heat exchanger was very corroded when removed. The second however did not look half as bad, but was cracked on the outside and when the boiler came on to anything above minimum it started banging and crashing about, hense the second replacement.

All is working fine now, but I really want to find the cause so I dont have the same thing happen again.

Incidentally, I have also had 2 radiators and a towel rail fail from small rust holes breaking through, one of the rads and the towel rail where under 5 years old.

Any help with this would be greatly appreciated, I am fairly sure I have enough inhibitor in it, and it has been suggested the boiler should not have died in 2.5 years even if the inhibitor was low.

Many thanks.

 

[ianmcd]

It does sound as though your inhibitor dosage is about right, too many installers do not calculate the thermal store capacity, however if the system was not cleansed properly when the new appliances were installed then the system will still corrode regardless of the inhibitor content I'm afraid

 

[MJGas]

I thought these heat exhchangers had a 10 year guarantee?

 

[Porque223]

I thought these heat exhchangers had a 10 year guarantee?

Then you can expect the heat exchanger to last around 10 years or somewhat less.
Based on the science of failure rates and reliability I'd think 2.5 years means a problem with the exchanger or something else is shortening its life. The problem may be finding someone who can give an unbiased opinion.

 

[ianmcd]

Couldn't tell you off hand what the gte is on the heat exchanger but can gte it will depend on the water quality

 

[Agile]

The holing rads is an obvious clue.

Some kind of pumping over effect I expect.

But all your postings have been totally devoid of any mention of the Installer or your fault diagnosing engineer!

Or is all this a DIY job that you have done?

Tony

 

[Gasguru]

Post links for the thermal store...the only one I can see on Albions site is to provide mains pressure hot water only. In which case the inhibitor in the store is just to protect the store water and is completey seperate from the boiler system. However, a lack of inhibitor would not cause cuch corrosion in such a short time.

Is the boiler operating as a sealed system or traditional vented system...ie. is there a small header cistern high up probably in the roof space?

Heat exchangers should have no problem lasting 10 years or more and radiators considerably longer providing the system is problem free. Even with poorly designed systems corrosion to your extent would not normally occur in such a short time. When similar problems have been reported the old issue of stray electrical charge has been raised. Is the boiler pipework bonded together? Worth googling.

Any pictures to post of the old heat exchangers/rads ?

 

[45yearsagasman]

+1 agree with Tony. The pin holing rads is a water quality issue.

 

[tjw1701]

Thanks for all your replies!

To answer a few of your questions:

This link should give you an idea about the system I have, it is a newer version but the priciple is the same. http://www.advancedwater.co.uk/header-012-088-MFDCYL.html

The thermal store is essentially a 210 litre tank with a ball valve in the top (which doesn't take well to the heat of the water I might add). The boiler take water directly from the bottom of the tank and pumps it back in to the top heated. The central heating via a seperate pump directly takes water from 1/4 the way up the tank and runs it around the radiators. The system is open vented. The water in the system can run round the boiler, the whole radiator system and the tank, hence the need for 12 litres of Fernox.

The system is self installed by me, and was flushed before first use. Some of the pipework has been reused but most of the rads are new (5 years). The boiler was fitted by my local plumber and he checked the work I had already done for the tank and rads.

The boiler was repaired by an engineer from the boiler manufacturer, he was not sure why the heat exchanger had gone again, and the water he removed from the system in the process was clean and clearly had inhbitor in it (could smell it).

Angile, could you tell me what you mean by a pumping over effect?

With regards to electrical bonding, there are earth bond straps but suspect they are insufficient as the original pipework was installed over 30 years ago.

The first heat exchange was rotten, it was clearly full of corrosion, but the second did not look blocked, which was strange because it was clearly faulty as the boiler could not run on anything other than minimum, and the casing had split.

I don't have any pictures of the exchanger, but will get a picture of recent rad as I still have that.

Do you think I should clean the whole system again?

With regards to water quality, the filler pipe is connected directly to the mains water supply (I have a softner and the first boiler repair man insisted it did not have softened water in it) I am supplied by Thames Water and the water is very hard. If there is a water quality issue, what can I do about it?

Many thanks!

 

[Agile]

Ignoring the boiler for a moment, you have pin holed rads! That indicates new oxygen being introduced into the system ( although it is odd than the water colour is clear!!! ).

BUT, although rare, there is always the possibility of the damage being caused by electrolytic action caused by an electrical fault creating currents through parts of the heating system. That can be emphasised by mixtures of different metals in the pipes and also by sections of plastic pipe.

That would need investigation by someone with a sensitive clamp type meter who understands what he is looking for.

One of the old posters on this forum told us about a block of flats near Bath where all the rads holed within a year or two. He never told us what the cause was ( presumably ) eventually when it was diagnosed.

Tony

 

[Porque223]

BUT, although rare, there is always the possibility of the damage being caused by electrolytic action caused by an electrical fault creating currents through parts of the heating system. That can be emphasised by mixtures of different metals in the pipes and also by sections of plastic pipe.

That would need investigation by someone with a sensitive clamp type meter who understands what he is looking for.

Try searching on
anodic series
or
galvanic series.

 

[dcawkwell]

Given the problem with the radiators.
You have a high rate of corrosion in the system.

Possible causes

1. Plastic non barrier pipe used in the system.
2. An electrical fault causing corrosion in the system.
3. A leak in the system causing the need for fresh water to come into
the system. Cut your header tank off. Does the water level start to drop?

 

[CBF]

Is your o/v system connected to the softner ?

if it is then there lies the prob with your boiler, WB MUST NOT be fed by softned water as you found out it will knacker the hex

 

[tjw1701]

The ball valve in the top of the store sometimes leaks and causes an over flow so I have a stop valve on the outside which I manually check periodically. It did lose water recently but of course most of this was on my lounge carpet! so at this stage it is hard to say how much is coming out of the system elsewhere. I am not aware of any significat leaks but I do have a few drain points which get very gunged up with green goo which I am assuming is a small weep.

With regards to the water, I do have a softner however the filler pipe has been connected to the mains water supply directly so is not softened.

There are no plastic pipes in the system, it is all copper. The rads are a mixture of old ones that were already in the house, and new ones from B&Q.

What sort of things do you think can cause the electrical faults you are describing?

Thanks.

 

[dcawkwell]

The ball valve in the top of the store sometimes leaks and causes an over flow so I have a stop valve on the outside which I manually check periodically. It did lose water recently but of course most of this was on my lounge carpet! so at this stage it is hard to say how much is coming out of the system elsewhere. I am not aware of any significat leaks but I do have a few drain points which get very gunged up with green goo which I am assuming is a small weep.

With regards to the water, I do have a softner however the filler pipe has been connected to the mains water supply directly so is not softened.

There are no plastic pipes in the system, it is all copper. The rads are a mixture of old ones that were already in the house, and new ones from B&Q.

What sort of things do you think can cause the electrical faults you are describing?

Thanks.

Usually an earthing fault allowing a small current to pass through copper and the water in the central heating system. Electric passing cause hydrogen to form using the water up in the system and bringing more water into the system. The production of the hydrogen also causes the copper and metal in the system to be corroded.