Heat Exchanger clean - a possibility?

[Agile]

I have got a leaking glowworn CI HE coming in on saturday for me to inspect. I will tell you what it contains.

The newly formed iron oxides are reddish and dissolve easily. After several months they trun into black magnetite which is much denser and more resistant to acids.

Tony Glazier

 

[alban]

I'm blinded by science! Well at least it's led to an interesting discussion - it obviously helps to have a Chemistry degree to be a heating engineer.

So ... is my best bet using FX-2 (as the stronger available chemical) for a lot longer in the flusher or to just bung it in the system for a week then?

To only flush the boiler seems difficult as the available connections are the ones direct to the boiler and there's no room to connect the powerflusher. There's just 'one lot' coming out.

(I hired the Kamco for £50 for a week so it seemed a lot cheaper than buying a new boiler and had to be done anyhow at some stage. Not much effort with sons running up and down stairs attending to rads. - payback time!)

Netaheat has one pipe leaving the top left, and tappings in the rear at top left, and TWO bottom right. In a pumped system ony one of the lower conns would be used so you could use the other as a drain point - if you can get whatever's in there, out.

OK so it is possible to directly intro some neat descaler chemical into the HE in situ and then drain it out? Can you actually get to these 'tappings' and pipes then? What about scouring with a wire brush or something?

Surely it cannot be beyond the wit of man (maybe mine tho') to unbolt and remove a big block of iron and clean it out?! Not exactly neuro-surgery is it? Call me Luddite or just tight but why chuck away something that's old and that probably just needs a good clean (could say that about Granpa!)? From what I've read in this forum condensing boilers are not such a 'great leap forward' either.

 

[Agile]

I dont see how you have reached the conclusions above.

You COULD try introducing the right chemicals into just the boiler and probably warm it up to help. But these are dangerous activities and I would never advise a DIY to use chemicals without the right training and protective equipment.

It would be safer to remove the whole HE and put it in the garden and fill it with 32% HCl and see what happens. But these are potentially dangerous chemicals! Do you want to blind yourself?

I really wonder why you want to spend hours when for £500 you can buy a new 28 kW condensing boiler in a shed and get someone registered to fit it for you. You would then save 20% of your gas bill. But the world is full of unusual people!

Tony Glazier

 

[ChrisR]

The tappings are on the back of the CI block. Though they're a few inches from the wall they would be quite difficult to use other than maybe as a drain. I'd use the pipes connected to it.

Spirits of salts is available widely (hardware shop), that's thirty odd percent hydrochloric acid in water. Apart from splashing problems you have to be aware not to put water into acid, always the other way round, or it might boil on the surface of the water and come get you.

The newly formed iron oxides are reddish and dissolve easily. After several months they trun into black magnetite

More a question of the oxidation conditions prevailing - iron can go straight to Fe304 without being Fe0, etc. Certainly the red one is favoured if there's lots of oxidising agent about. Temperature, pH make a difference too.

 

[alban]

Like a dog with an old bone.
The cold feed seems to go to the back of the boiler - is it likely to go direct into the HE or somewhere else (where could it go?) then into the HE? If so, could I intro the HCl into the HE via the cold feed pipe at the F&E tank opening and then just flush through with water after leaving it for a few hours? Maybe a crazy idea but there you are.

 

[ChrisR]

NO, the HCL would be too hard on the copper if left for any length of time. Kamco do an "inhibited" Hcl which they sell (I think) as HD something. It says it's for heat exchangers and not CH systems - even though it isn't the highest octane stuff.

Thinking laterally for a min you might find that the gas pressure (set in the boiler) is too high, or even if not TOO high, lowering it should quieten things a bit. Not something you'll be able to measure without a U gauge and hundreds of seconds of training.

You could however measure the gas comsumption on full burn - if the pressure has drifted high it would show. Assuming you have an imperial meter, time one revolution of the 1cu ft dial, divide 1093 by the number of seconds and you'll have Kw input. The correct input figure will be on the boiler/book. It'll be a range , 12-18kW or so for a "10-16" boiler.

 

[alban]

Resurrecting old point on Netaheat mk2F.
Sure malfunction of boiler due to over-heating as putting doubled alum. foil between control 'box' and boiler bottom seems to eliminate failure and boiler chugs along OK but hot++. Prob affecting function of pressure switch as it seems to fail at that point in the cycle but OK when cooled down.

Cold feed goes to one of connection holes in back of HEx and vent comes from pipe issuing from top of HEx.
Q. is, can I use a powerflusher to intro and circulate Kamco's buffered HCl thro' HEx using the Feed and Vent which are easily accessible? Is it likely to 'get' to the bits that need de-scaling in the HEx or is there some mysterious routing within it that will prevent it?
I could break into flow and return but that's not that easy.
I thought that I could leave system 'off' and mot. valves would prevent HCl going to rest of system and thus opening up a million leaks!