Grant Combi 90 oil boiler

25 Sep 2011
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United Kingdom
Calling all Heating Engineers

Have a Grant Combi 90 oil boiler which was installed approx 10 years ago.

The boiler decided to spew its contents onto the kitchen floor recently and a heating engineer confirmed that the boiler had corroded and was beyond economical repair.

There are 3 connections to the top left hand side of the boiler and one larger connection on the bottom left hand side. It is this bottom connection which has corroded. From the manual it would appear to be the central heating return.

I believe that it should be possible to remove the outer casing and have the boiler welded to repair this corrosion however the heating engineer who looked at it said that the boiler was beyond economical repair.

I can appreciate that there may be considerable labour involved in removing the tank from the casing hence the suggestion of a new boiler.

I work as a mechanic and am fairly confident that I have the ability to strip the boiler down and fabricate the tank myself (although I can't see the extent of the corrosion for the outer casing at the moment). The boiler's knacked at the moment anyway so nothing would be lost if I was opening up a can of worms.

Would I be embarking on a road to nowhere or from your collective experience would you consider this repair possible? I can upload photos if you think it worthwhile. Obviously if the repair was successful I'd get a heating engineer to check it out and recommission prior to using.

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If your confident enough and the boiler metalwork can stand the welding?, why not give it a go. Ive done several with a welder friend.
It is only a steel box inside a steel box.

However, unlike cars etc there will be masses of guey sludge in the bottom, which will not be conducive to getting a good quality weld.

Oil boilers are pretty basic but if you were paying time and labour from a heating eng it would definitely not be worth it. If it is your time at stake then it is worth a punt, assuming you could not be using that time productively elsewhere and getting paid for it.

Personally, I'd bin the thing and get a new one. Making sure that any contamination from sludge was removed and the cause identified.
if you were to remove the unit, cap all ports and then pressurize it with air, spraying leak decector over it until you locate the leaky'll then repair that leak and re-fit the unit.

6 weeks later it'll probably leak somewhere else.......thats the law of sod!

if, as has been said, it is done on your time, then it is well worth a try, but don't pay someone to do it.
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Thanks for your comments guys. I'm gonna go for it and try the repair.

Might as well, nothing to lose except time. Reckon some of the other bits might be resellable on ebay anyway, burner, pump might as well get it stripped down.

I'll see how it goes anyway and post the results.
Quite possible to fix it.
Just not economical for the heating engineer to fix it.

Drain down the system. Disconnect the boiler.
Tip it up and then weld away.

Corrosion has probably been cause by a leak that hasn't been addressed
at a regular service. In fact there is probably very little leaking. Probably
only take a minute or two to fix it.

Oil boiler should last 20 years given a quick check once a year.
It is worth mentioning that the rust was probably caused by condensation. This would happen due to low temperature water in the return pipe created by running the boiler with the thermostat turned down or the system not balanced to give a temp of 11 degree centigrade difference between flow and return

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