Main Medway Super Scaled Up?

[Mitch]

I've got a 'Main Medway Super' multipoint gas water heater which seems to not to be able to provide 'piping' hot water any more, I've adjusted the dial on the front (which I think just reduces the water flow) to raise the temp but now theres no more adjustment left and the water is not really hot. I'm wondering if its scaled up. It was installed in 1999 and has been well used since then. Are there any other possible causes (I know its cold outside but this has been the case over last 18 months) and if it is scale what the best way to clear it; caustic soda or buy a new heat exchanger? I want to keep the boiler so I'll have to do whatever it takes.

Incidently this is the first fault in 14 years as it has not even got a circuit board or mains connection, love it!

Thanks

M

[John Williamson]

Has it been serviced regularly, or just left to its own devices? Burners lose efficiency over time, and if they're running rich, carbon gets deposited on the heat exchanger, which reduces the heat transfer rate. If they run start to run lean, then the heat from the flame is reduced.

As for whether it's scaled up, you don't mention if you are in a hard water area or not.

[Mitch]

Its had a clean of the combustion side of the heat exchanger but it it was only light dust and grit (and the obligatrory spiders at bottom).

We're in a hard water area (Watford). I'm trying to establish if it's viable to descale a heat exchanger if its scaled up.

Thanks

Mitch

[docholliday93]

On Monday, January 21, 2013 8:38:19 AM UTC, Mitch wrote: =20

eat > exchanger? =20 I'd have expected to use something acidic for descaling, rather than causti= c soda. The commercial ones seem to use citric or sulphamic acids, or the folk reme= dy uses acetic acid (in vinegar). The important thing is to have something = which reacts with the limescale to produce a soluble salt, while not reacti= ng with the heat exchanger, so it would be useful in thinking about this to= know what the heat exchanger is made of.

[geoff]

Hydrochloric (HD) Phosphoric (FX) or, yes Sulphamic

Look at one of the sites such as Kamco

[currie.chris4]

I've got exactly the same heater and issue as you Mitch its very frustrating especially the time of the year.

Geoff the link you attached is very useful.

In terms of descaling what would you recommend and also is it a job someone with little experience should not take on or is it a simple process Without taken the whole heater apart?

[geoff]

In message , [e-mail] writes

Unless you have access to a suitable pump, I would have thought that you would be best removing the heat exchanger and use a tube and funnel

The important thing is to keep the acid moving so that you don't end up with neutralised spots

HD and FX2 from Kamco have an indicator which will give an indication as to how much oomph (technical term) it has left

[currie.chris4]

Thanks Geoff appreciate your recommendations and advice.

Would I just need to turn the heater off to remove the heat exchanger or both heater and gas supply into the unit?

[geoff]

In message , [e-mail] writes

I would have thought that to be safe, you should remove gas and electrical supply as (I think) you have a pilot flame there which you will need to relight later

I'm not a fitter

[currie.chris4]

Thanks Geoff

[Andrew Gabriel]

especially the time of the year.

with little experience should not take on or is it a simple process

I used to have to descale mine about once a year. Take the heat exchanger off, and stand it upside down in a trough or large washing up bowl to catch spills (or old bath if you don't care about the dye staining it). (Sulphamic acid will wreck polished finish on enameled baths.)

Mix up some Furnox DS-3 (sulphamic acid plus indicator dye), and pour it into the the heat exchanger. Works better when it's hot, but it may froth over, and the spray generated by the frothing is not pleasent, so do this in a ventilated area. After a minute, pour it out and back in again, to keep it moving. Keep repeating this whilst it's still giving off carbon dioxide, and then for 5 minutes more when you can't see anymore. If the dye goes from yellow to blue, discard it and mix up some new DS-3 solution.

I would suggest replacing the O-ring seals on each pipe end when refitting. A few days after refitting, take another look inside to make sure there are no leaks, as a leak here will rust a hole in the case, which makes the unit unsafe and a write-off.

The Main Medway I bought around 2000/2001 (can't recall exactly when) has the heat exchanger internally teflon coated, and I've never needed to descale it yet.

[Mitch]

Excellent, thanks for good advice, hopefully I can do it before SWMBO notices!

[docholliday93]

=20

myself, but last time I was looking for descaler the only one I found (apar= t from the domestic ones for kettles etc.) was Fernox, which is Sulphamic a= cid; it's nice to know where to get other types.

[warrior]

replying to Mitch, warrior wrote: Mitch.You need a fair ammnunt of hHydrochoric Acid. (Spirit of salts.pour it in with a funnel with a large bowl water to stand the heat exchanger in.Wear gloves and mask and gogles. Do it near a drain and cold tap.My no is O7549451063

[tabbypurr]

He's been waiting nearly 7 years for that advice. Maybe use a saner portal to news:uk.d-i-y like google groups.

[Brian Gaff (Sofa)]

Google sane??? Brian

[harry]

You're probably right. The only cure is to chemically clean it which involves disconnecting the water side. But you might find it then leaks, the scale having covered up the leaks. The only external clue is abnormally high flue gas temperatures.

But first check that enough gas is getting through There should be a test point for gas pressure but you need to know the correct pressure.

Also the nozzles for gas on the gas burner may be partially blocked. Or even insufficient air if the air intake is blocked.

You be careful with caustic soda it can heat very rapidly if a large amount is added to water. Wear goggles.

A proper descaling chemical has an inhibitor which prevents it attacking metal

[bernie]

Give me a call

[alan_m]

You probably need a time machine to go back to be of any help for questions posted 7 years ago.

[Brian Gaff (Sofa]

Yes having looked at this I have to assume that users of that particular forum to read useenet must be innumerate. I can plainly see the date of the original post on that page with my screenreader, so why not with a pair of working eyes? Brian