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Cleaning a heat exchanger?

A recent thread of mine on here led to the probable diagnosis of a scaled/blocked secondary (water-to-water) heat exchanger in my WB

24CDi combi.

Given the potential uncertainty surrounding the fault/cure, and the fact that I am a tight Northerner, I was wondering about ways to avoid/ delay the =A390 expenditure on a new heat exchanger.

In particular, I wondered about removing the heat exchanger and at the very least checking and testing it - but also perhaps cleaning/ unblocking it too. Any tips/suggestions/ideas as the ways to go about this? I am assuming it will require more than physical cleansing, perhaps chemical cleansing to really dislodge any crud in there so I was wondering what I should get and from where?

Feel free to tell me to blow the dust of my wallet if this skimping is really not worth the hassle (the boiler, and heat exchanger, is 11 years old by the way).

Mathew

Reply to
Mathew Newton
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24CDi combi.

Given the potential uncertainty surrounding the fault/cure, and the fact that I am a tight Northerner, I was wondering about ways to avoid/ delay the £90 expenditure on a new heat exchanger.

In particular, I wondered about removing the heat exchanger and at the very least checking and testing it - but also perhaps cleaning/ unblocking it too. Any tips/suggestions/ideas as the ways to go about this? I am assuming it will require more than physical cleansing, perhaps chemical cleansing to really dislodge any crud in there so I was wondering what I should get and from where?

Feel free to tell me to blow the dust of my wallet if this skimping is really not worth the hassle (the boiler, and heat exchanger, is 11 years old by the way).

Mathew

Reply to
Doctor Drivel

A couple of packs of supermarket kettle descaler would probably work as well if you're really tight. Leave overnight >drain >flush with a hose >put the acid back (or a fresh lot) I think the danger is that the crud may be masking leaks, which might start to flow freely once the corrosion has gone. I remember descaling a rad on an old Morris Minor once (anti freeze wasn't standard back then). It functioned perfectly for a few days, and then the bottom fell out

Reply to
Stuart Noble

Plate heat exchangers are stainless steel.

Reply to
Doctor Drivel

Thank you both for the suggestions. One thing I didn't specify was that it is actually the primary (CH) side of the heat exchanger that is suspected as being blocked... do you think this would be down to limescale? Or crap from the CH system? It's had inhibitor for the past

7 years, but before that I really don't know. I fitted an inline strainer a couple of years ago - it'll be interesting to see if that's got anything in it.

Mathew

Reply to
Mathew Newton

Thank you both for the suggestions. One thing I didn't specify was that it is actually the primary (CH) side of the heat exchanger that is suspected as being blocked... do you think this would be down to limescale? Or crap from the CH system? It's had inhibitor for the past

7 years, but before that I really don't know. I fitted an inline strainer a couple of years ago - it'll be interesting to see if that's got anything in it.

Mathew

Firstly, put a Magnaclean filter on the return to the boiler. Use cleanser to remove the crud. Use DSL to clean the plate heat exchnmager. After cleaning use a hose to clean it out. Re-fill with OX-100 in the system after a few flushes.

After one month check the Magnclean filter and clean if necessary. After 2 months check again. If still crud then keep cleaning filter ever 2 months until clean. Then clean every year.

Reply to
Doctor Drivel

I have to do this job periodically on my Ariston Microgenus. Speaking as a tight-fisted southerner it's definitely worth it, and I remember the joy throughout the household the first time I did it and restored full flow and heat to the shower! Ah the rewards of DIY.

Anyway, I agree with Drivel that DS3 is the stuff for descaling. However, sometimes in my case the clogging is on the primary side due to iron oxide (rather than limescale on the secondary side). In this case I don't know of any chemicals which will shift it, and it's just a matter of flushing it through at as high a pressure as you can manage, coupled with some knocking about to dislodge stuff. By the way, I find a cheap drill-attachment pump with a couple of suitable bits of hose is good for circulating hot DS3 solution through the heat exchanger.

If it is black iron oxide causing the problem then you don't have enough inhibitor in the system, and the whole system will need a flush through and fresh inhibitor.

I've managed to keep mine going for the last five years like this. It's a couple of hours work, most of which is just leaving it soaking.

Cheers!

Martin

Reply to
Martin Pentreath

The down side of descaling the the only DHW heat exchanger you have is:

1) the down time on the boiler whilst you are doing the job. 2) if it springs a leak either internally or externally your shafted. 3) a new one will have new washers and O-rings to make a good refit.

As a pro the above weight heavily against me. As a diyer you might well find that some descaler (DS3, patio cleaner, kill roc etc.) does the business. It is academic which side is the main culprit as once it's in the acid both sides will be fixed.

All the best

HTH

Reply to
Ed Sirett

I have to do this job periodically on my Ariston Microgenus. Speaking as a tight-fisted southerner it's definitely worth it, and I remember the joy throughout the household the first time I did it and restored full flow and heat to the shower! Ah the rewards of DIY.

Anyway, I agree with Drivel that DS3 is the stuff for descaling. However, sometimes in my case the clogging is on the primary side due to iron oxide (rather than limescale on the secondary side). In this case I don't know of any chemicals which will shift it, and it's just a matter of flushing it through at as high a pressure as you can manage, coupled with some knocking about to dislodge stuff. By the way, I find a cheap drill-attachment pump with a couple of suitable bits of hose is good for circulating hot DS3 solution through the heat exchanger.

If it is black iron oxide causing the problem then you don't have enough inhibitor in the system, and the whole system will need a flush through and fresh inhibitor.

I've managed to keep mine going for the last five years like this. It's a couple of hours work, most of which is just leaving it soaking.

Cheers!

Martin

Reply to
Doctor Drivel

Hi Ed, is this right? I've never found DS3 (or any other chemical) dissolves iron oxide, which is the main culprit on the primary side. 'A' level chemistry is a long way off now, but I think it's not easy stuff to remove chemically.

Cheers,

Martin

Reply to
Martin Pentreath

Ahh... perhaps we're not all that different after all! ;-)

Now you're talking - that's what I like to hear. Your positive experience has convinced me to at least give it a shot.

Ed's mention of downtime and leak potential are valid points but the GF has been reminded she has showers at work, and if the heat exchanger springs a leak I will convince myself it was about to happen anyway and hence justify the =A390 for a new one. Regarding o-rings and fibre washers I've got a pack of the former so will get the latter also to be on the safe side (the official WB part/bag is around =A37.50

- are they really that special or will any generic bag of suitably sized fibre washers suffice?)

B&Q sell Fernox DS3 by the small tub for =A33 so it's worth a shot with that anyway. As for the drill pump I'll give that a go also - tight fistedness is overruled by opportunities to buy new tools so I'll pick one up from Machine Mart (=A313 and stainless steel innards so should last me a while).

Yeah I'll put some fresh. The system has been topped up a few times over the years during radiator removals etc so it could probably benefit from some.

Finger's crossed...

I may find it's not bunged up at all in which case I can then focus on buying a new diverter valve instead!

Mathew

Reply to
Mathew Newton

If you are talking about rust, (iron oxide?), then Muriatic Acid ( AKA hydrochloric Acid ) will strip rust from steel/iron. I don't know what your heat exchanger is made of so don't blame me if it full of holes after this treatment ! A form of Muriatic acid is sold in builders merchants as Brick Cleaner if you want to give it a try. I have used this, cold, on bits of rusty steel from an outboard motor with good results.

Ian.

Reply to
Ian French

Hi Ian,

Again, stretching my recollection of schoolboy chemistry here, but the black stuff you get in heating systems is iron I oxide, brown rust is iron III oxide. What the difference is I forget, but I think the black stuff is harder to dissolve.

Matthew, I can conclusively prove that southerners are more tight- fisted than northerners. I've always used the same O rings without a problem (never occurred to me to get new ones, do you think I'm made of money?) and I got a drill pump from Toolstation for a fiver (part number 23710). Good luck with the boiler.

Cheers!

Martin

Reply to
Martin Pentreath

I dont have any answers to offer on this, just a couple of points that might possibly be worth looking up. Oxalic acid is used to remove rust stains, and rust convertors are usually phosphoric acid based.

NT

Reply to
meow2222

Hmm... Now you've made me look all flash throwing my money around. I did see the Toolstation one but figured that long term I might be better off with the more substantial MM version

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- at least it's got some specs that sound good. You get what you pay for right? Whoa.. the sun has clearly got to me. Maybe I'll call in to TS and have a closer look.

Mathew

Reply to
Mathew Newton

No they won't work. The volume of scale which builds up in a blocked plate exchanger way exceeds what you find in a kettle. A tub of DS3 will be much cheaper than the quantity of kettle descaler you would require, and it's not mixed with sand and other things used to bulk out kettle descaler which you don't want in a heating system, and it contains a colour change indicator so you know when the mix needs to be replaced.

You can use DS3 around the house for other descaling purposes, but not on plastics (it makes some plastics go brittle).

The bottoms fell out of lots of Morris Minor's. I know someone who is still keeping one going (last time I bumped into him anyway). If you see a Morris Minor with a penny farthing bicycle rack driving along, I doubt there's more than one in existence.

Reply to
Andrew Gabriel

Hi Martin,

Yes, on reflection, what you need is EVAPORUST !

No, I am not joking, see this link

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Reply to
Ian French

The heat exchanger is probably a stainles steel plate heat exchanger (HX). Dowload service manual from the WB site for you model and check. Check it isn't a failed water pressure or temperature sensor If it is a sceled up HX then you could do this yourself - no gas connections involved.

Find the right fittings for the HX connectors, both primary and secondary side.

Take the HX out, connect rubber hoze to HX inlets, outlets and see if water flows through

Go to a DIY and butuy a small tub of sulphamic acid descaler (powder) such as Fernox DS-3 or similar. Citric acid descalers are less vigorous and very slow on lime scale ( but less harmful top plastic kettles etc)

Follow instructions - best used hot as reaction is faster, and rig up some form of small break tank and pump. thgis is to ensure fresh acid keeps passing through the heaat exchanger.

Do this outside - and well ventialted area and follow H&S precuations ( eye protection, rubber gloves etc) & common sense , no peets kids etc nearby etc.

FWIW

Reply to
rdd

The CH flow pipe is heating up also so I've narrowed it down to a sticking diverter, or blocked heat-exchanger (on the basis that this could cause divert bypass).

Yeah, I'm going to give it a go and whilst it's off I'm hoping I can get a finger inside a divert valve port and manually move the slider.

I'm all good to go on this. Got the descaler, pump and bits+bobs.

Thank you, and everyone, for the help. Will report back how it goes!

Mathew

Reply to
Mathew Newton

The particles tend to be an mixture of both Black Oxide (which will need quite strong acid to reduce) and scale which HCl easily removes.

In my experience there is enough frothing on the primary side of a DHW to mean that using the acid is worth while.

Reply to
Ed Sirett

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