Heat Exchanger clean - a possibility?

[alban]

Tried chemicals, descaling, powerflushing with chemicals, changed pump (and now up to setting 3), checked mot. valves all to try to stop boiler overheating and cutting off when boiler therm. turned above Min. setting (this occurs very quickly before water has fully heated up). Fan looks OK too. Presume some clogging in Ht Exgr and reduced flow causing problem?? Mild kettling still despite 3 descales. I've neglected it for 18 yrs so it's payback time.

I'm wanting next to clean the HE out (it's sound) on my old Netaheat (MkIIF) but couldn't see a drain plug in its base when heating engineer came round to service it. Just a bolt to secure the wall of combustion chamber on each side. Diagram on Partsarena shows no drain plug but shows two plates bolted on to each side of the HE both with a seal. If these are removed can you gain access to the main chamber to de-gunge it without removing whole thing from boiler? I know re pos. press. /seal dangers thanks to warnings here.

Also how do I identify a bypass in the system? It's an old (20+yrs) open-vented one with two straight zone valves and a pump all in airing cupboard with boiler downstairs. The bathroom rad used to get warm when only hot water on - does this mean it IS the bypass? Last year plumber changed it for a towel ladder rad. and has obviously 'done something' with the pipes - could he have inadvertently altered any bypass arrangement leading to our boiler overheating problems? Have opened rad up fully - no difference.

 

[bathjobby]

Haven't I just replied to this elsewhere !

 

[kevplumb]

20 yrs old cmon bite the bullet and put it out of its misery

 

[ArtfulBodger]

20 yrs old cmon bite the bullet and put it out of its misery

That's what I thought, plus for a massive HE like that to block the whole system must be full of craaaap

 

[alban]

Bathjobby - yes you did address this in my last thread but couldn't see any kind of drain plug at base of HE - as I said just these plates on each side plus 2 bolts holding on combustion chamber wall.

Ditch it? 20+ years old yes, but working OK in all other respects. Low income due to health (sob story) means a replacement for £1-2K or so is very daunting at present. Why do you think I'm trying so hard? I don't enjoy it, honest! Still enough of the play for sympathy!

Cheers for the time and thought you guys put in for free to help out.

 

[ArtfulBodger]

Bathjobby - yes you did address this in my last thread but couldn't see any kind of drain plug at base of HE - as I said just these plates on each side plus 2 bolts holding on combustion chamber wall.

Ditch it? 20+ years old yes, but working OK in all other respects. Low income due to health (sob story) means a replacement for £1-2K or so is very daunting at present. Why do you think I'm trying so hard? I don't enjoy it, honest! Still enough of the play for sympathy!

Cheers for the time and thought you guys put in for free to help out.

There definitely is a drain off for the HE - look harder!

 

[Baxi-Remeha]

low income due to health.........get a grant

 

[bathjobby]

Alban, the real point about my comment that you have another thread running with this is;
We give our time freely to reading through these posts and trying to help people. If the people we are trying to help are posting multiple instances of the same problem then they are showing total contempt for our efforts by increasing our 'work load'.

 

[doitall]

Dang my old boots why didn't I think of that bathjobby

 

[bathjobby]

Whatever that means !
Think I'll go back to tending the garden and leave all you guys to pay my buddies their 'emergency plumber' fees..........

 

[doitall]

Whatever that means !
Think I'll go back to tending the garden and leave all you guys to pay my buddies their 'emergency plumber' fees..........

Bit dark for gardening

 

[Agile]

Back to the original problem.

You say that its been power flushed and descaled and then next you mention a heating engineer.

If you would describe in detail exactly what was done and how then I could tell you what was wrong.

Example, an old lady I know ( 50G ) had a Vaillant T3 with a scaled up HE, because she is a pensioner I let a friend of mine try to sort it out for her as they do charitable work together and he would not charge her.

He is very good with electronics and electromechanics but I am disappointed with him on boilers. A lot of the problem is he will not listen because he thinks that he knows more about it than I do. I kept on telling him the main HE was scaled up but his reply was that he had descaled it himself "so it was ok" and he refused to discuss it further.

The blockage was preventing the flow switch from operating. My friend failed to fix it in spite of hours on the phone with me. My engineer using his training in dealing with this problem fixed it without assistance even though he has only been in the trade for about a year.

The lady finally got fed up with him and pleaded for me to sort it out. I sent my engineer round and he descaled it with the correct chemicals. Apparently my friend had used formic acid sold to descale kettles which is useless on iron oxides.

I saw her today and she said she did not love me any more because the boiler is working so well she is in love with it instead!

Tony Glazier

 

[chrishutt]

Tony, what is the right chemical to clean heat exchangers? I've also tried unsuccessfully to descale Vaillant HEs, presumably using wrong chemical.

 

[Agile]

The chemical required depends on the type of contamination in the HE.

An old Netaheat or similar in an otherwise clean system usually has calcium and magnesium carbonates and complex carbonates with some iron atoms.

Hydrochloric acid is good on both of these but only suitable if the HE is outside! Otherwise sulphamic acid is best and bought as DS3.

Iron compounds respond well to citric acid, DS40 is mostly citric with some malic acid.

I use a mix of DS3 and citric acid in proportions depending on the amount of iron compounds likely, typically 4:1 initially. Sulphamic acid is not very effective below 80*C.

Kettling is usually caused by lime scales and treated as above. This can happen due to faulty commissioning on combis and most likely on 28 kW units rather than 24 kW when the heating output has not been set to the demand.

Most newer sealed systems are usually only blocked by iron compounds and here citric acid products are suitable. And to keep Keith happy the FX2 is fine. Again best when at about 60*C if the gassing can be controled.

I give all this information for professional use NOT for DIY as full body protection should be used and knowledge of dealing with spills and chemical burns to the skin is essential. And of course eye protection is needed.

Tony

 

[alban]

quote]Alban, the real point about my comment that you have another thread running with this[/quote]

Had posted again in older thread but thought it was 'dead' and therefore not looked at, my mistake. Noted now your reply to that thread - seems that to see new responses have to hit 'refresh' button. Also seemed to be a different question I was asking now.

There definitely is a drain off for the HE - look harder!

I looked hard - I can't see anything remotely like a drain! Netaheat MkIIF - how certain are you there's one?

If you would describe in detail exactly what was done and how then I could tell you what was wrong.

Superfloc 2weeks normal cycle
Drain through
No change

DS-40 7 days normal cycle.
Drain through
No change

New Pump on max.
Slight change

Heating Engineer - service and check up. "Could be this or that. New boiler mate" Fan seemed OK, not clogged. HE - 'sound'. Pressure switch dodgy but boiler cycles normally on min.
No change

2 rads off - crud++. Knackering so -
Change in approach!

DIY Powerflush following Kamco instructions with SX2 twice each time for an hour or so. Poor result ie little crud displaced, some gas produced but mild kettling still present. Linked Vent and exp pipes but closed connection when flushing individ. rads. Now wonder if there was a 'bypass' I didn't close leading to poor flushing? Can't identify it.
No change.