heat exchanger regularly blocked up ?

[scooter]

Hi there guys,
I have a halstead ace high boiler which keeps losing the hot water every 6-8 weeks. Seems to be the dh heat exchager is getting blocked with black flakey bits (oxide?) which i have to clean out to get working again. I know the heating system is clean as i have used cleaners and inhibtors and also fitted a Magna flow to the return flow as recommended which is clean when ever i check. Also its the hot water side of the heat exchanger which is getting blocked.
Can anyone tell me where the black bits come from and how i can stop them blocking the heat exchanger.( the black bits are megnetic).
Its a real pain having to keep cleaning it so any help from you guys would be much appreciated.
Thanks scott...

 

[newbie1]

your heating water and hot water do not mix and you could have pure spring water in your heating system and it wouldnt make the blindest bit of difference to your hot water as the water comes from the main as far as i know i would guess your problem needs a closer look at the dhw exchanger

 

[stevetheplumber]

if theres black bits in the hot water side you would have black bits in the hot water comming out of the taps only other thing i can think of is something in the boiler is breaking up and blocking the heat exchanger

 

[Puddle]

Well if black iron bits being found in hot side of plate heat exchanger you would expect bits to be coming out cold taps also,the hot taps are probably being filtered by boiler
The first thing to look for is any old steel pipework on cold water inlet to boiler ,if so this is your problem,maybe when combi replaced cold supply linked through old tank pipework or a length of the old heating pipework was used to run cold supply to new boiler position, maybe fit a strainer to ciold water inlet
But do double check it is the hot water side and not the heating because the ace/ace high does get blocked very easily

 

[scooter]

Thanks for replying guys ,
its definately the dh hot water side of the heat exchanger thats getting blocked and ive checked for any steel pipe work being used which there isnt, and also it does come through the hot tap (very small amounts after cleaning the heat exchanger). So would this mean that its coming from inside the boiler somewhere ?
If anyone can shed some more light on this id be really greatful,
cheers scott.

 

[migoplumber]

why not try to put a filter on the cold main going into the boiler. to check the feed is clean. if it is then that would suggest a problem with the heat exchanger itself going into meltdown

good luck
shaun

 

[Bernie2]

I know it may sound a daft question, but are you talking about the heat exchanger fins or the internal water ways?

Funnily enough if its the fins try looking up Sulphide's or "Google" black dust. It may be that your using natural gas with a high sulphur content and its reacting with the fins.

Possibly on the DHW side because that is the side that gets the most frequently concentrated high burn rate and also in the Summer the only side you use.

Have a look at HSE Report 287/2000. Its about Sulphide's. Its interesting.

I've worked on jobs and been required to re pipe whole houses out because of Sulphide's black dust and the houses where only about 10 years old. So the pipework wasn't old. But the stuff was chocker where a pipe reduced and lined the inner walls of the pipes. One tap and it came off in cobs.

It looked as though somebody had annealed the inside of the pipes and left the oxidised scale on.

If its the internal water ways, are you using a water softner renewed wih salt?

Is your boiler suitable for softened water?

What is the Ph of your local water? Is it affecting the water ways when heated?

Drop the bits into a pan of water and boild them up, if they stay there after you have boiled the water they are not calcium bits depositied by hard water.

The problem is its all a complicated mixture of chemicals unless you know what the bits are actually made of.

But because its so rapid one would tend to think what ever is causing the reaction must be there in quantity and should be fairly obvious unless its water or gas born chemicals.

Hard water corrodes steel faster than soft, depending of course on a few other things.

I would look up on a chemical website about what corrodes or deposits layers of the material your talking about, on stainless steel heat exchangers, if you say its not a mixed metal system.