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It might be worth checking the make and model, since although you are correct that the majority of combis work on the same principle, there are a few that deviate from the norm.

Probably. If by "furred" they mean the HW HE was obstructed by hard water scale on the domestic hard water side, then you are right - the magnaclean will have no effect. If they mean the HE was blocked on the primary flow side by sludge, then it may help. (although fixing why the primary side is sludging up in the first place would be better than trying to treat the symptom).

British gas then ;-)

Either than, or the plumber in question had not really thought through the chain of events too carefully!

The two water paths are separate, but they're not completely independent systems. To heat hot water, the "central heating" water is heated by the gas and then, instead of going round the radiator circuit, it's diverted through a heat exchanger to transfer its heat to the hot water side.

Depends on what the actual problem with the heat exchanger was. If it was blocked on the hot-water side then the filter seems unlikely to help (unless there's some odd effect where sludge in the other side causes less-even heating and consequent problems). If it was blocked on the other side, which is actually part of the central heating water, then a magnaclean doesn't seem unreasonable.

Pete

Spooky - I thought the very same :-) Bunch of bandits IMO.. At least Dick Turpin had the decency to wear a mask...

No, the type you describe was always relatively uncommon and AFAIK no-one makes that type any more (i.e. as high-efficiency/condensing boilers). Much more common is the arrangement whereby the primary gas->water heat exchanger heats water that goes either to the central heating or to a secondary heat exchanger that heats the hot water. These secondary heat exchangers are usually plate types (PHEs) and these are susceptible to scaling ('furring') up on the secondary, domestic hot water, side, or to getting blocked up with gritty magnetic debris on the primary side from the water that also goes round the radiators. In my limited experience of this phenomenon it seems to be Baxi Combi 80 or 100s and Potterton Performas (same model, different badge) which are susceptible.

Sounds like a good idea. However I fitted a Fernox Boiler Buddy (similar idea - magnetic filter) to one of my victim machines and its PHE still got blocked! A quick swish round the system with the powerflushing machine bought several months' trouble-free operation but the problem eventually recurred. Fortunately with these boilers one can swap the PHEs in a matter of a few minutes, and Norstrom (who make my flushing machine) do an adaptor specifically for power-flushing these PHEs (I wonder what that tells us about them!). So now I keep a cleaned one in the van and swap it for the one in each latest victim boiler as I come across them!

Interested to know what a 'sonic cleanse' is.

I think Magnaclean-type devices aren't for protecting radiators so much as protecting the narrow waterways in boilers' heat exchangers - including the primary gas->water heat exchangers in modern boilers.

I think your mother's engineers may be making an honest and sensible attempt to deal with a problem not just immediately but in the long term.

Checked again with my mother and it's a Ideal Boiler HE30 and yes your correct it's got a Plate Heat Exchanger .. (accordingly to the manual she has).

We're not sure what a sonic cleanse is also ... perhaps some sort of ray gun

As good as ever a reason for not having a combi boiler. With a DHW cylinder and an immersion heater she would still have had hot water at least.

I imagine it's an ultrasonic cleaner, which could well help.

I had the primary (i.e. the closed loop) of my DHW (on a Halstead combi) block last year with the usual black sludge and debris, corrosion products from radiators because of insufficient inhibition. Replaced the heat exchanger and put in a Magnaclean (and added inhibitor). Within about six months it was misbehaving again. The Magnaclean had certainly trapped a fair amount of black oxide, but the heat exchange primary was blocked again. This time I tried a chemical clean on the removed heat exchanger using formic acid (kettle descaler) plus flushing. Not the ideal chemical approach, hydrochloric acid (brick acid) would be better but this can be bad for stainless steel heat exchangers. It's been OK for a while; perhaps the Magnaclean is taking a while to collect the existing circuit debris. In an ideal world you might flush and re-dose the whole circuit, but that wasn't practicable for me at the time. There doesn't seem to be a problem with limescale buildup on the secondary (domestic hot water) side in my system; I don't think the heat exchanger really runs hot enough.

I'm reasonably happy with the Magnaclean, though. Quite well designed and easy to clean out (it comes with isolating valves) and it is a convenient point to add inhibitor, slightly more convenient than via radiators.

I tried fairly concentrated HCl on the PHE and on a sample of the gritty magnetic crud blocking one up and it had no effect on them.