Grant 70/90 Multipass - Leaking

17 Apr 2004
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United Kingdom
Hi All

I think I know the answer to this one, but just want to explore all options before facing a painful bill.

I have a Grant 70/90 multipass, sealed system oil condensing boiler. It was installed about 17 years ago. Water locally is very soft and not aggressive.

Boiler has started to leak small pool of water underneath. It's floor standing and difficult to get to, so hard to do any easy investigation. I'm coaxing it to run at the moment by re-pressurising and bleeding off the air.

I'm guessing the jacket has failed and the boiler is probably US, but before I condem it is there anything else that's worth investigating. Assume it has a heat exchanger (?) but can't seem to find an exploded diagram. Presumably once the burner and cover was off this would be easy to check.

Any ideas, or am I just kidding myself and need to fork out £1500 plus fitting....Gulp

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Multipass isn't a condensing boiler btw. Welding doesn't usually work.
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Hi All

Just a quick update on this one for anyone searching threads in the future. I know the boiler is on borrowed time but put a 500ml bottle of Fernox F4 in the system about a week and a half ago. For now, no leaks, boiler hold pressure etc (touch wood). So at least hoping this buys me some time to save the pennies. Luckily if worst happens, where boiler is located any bad leak will just drain away.

Thanks for all the help.
Hi All

So I wanted to update and resurrect this thread for anyone who searches in the future. So two years ago wasn't a great time, and as advice above I used Fernox F4 (twice), and it struggled on unit April last year, when trying to fill it just flooded the bottom of the boiler.

Because the new replacement Grant boiler was expensive, and due to the increased with would have meant new utility cupboards, worktops etc, I decided nothing ventured and stripped it down to see what the issue was. On the sides,and back are dimpled section that look like the inner and outer plates are welded together. Mine had gone on the weld of the dimple on the back plate. To prove this I blanked off all connections apart from one, and put a hose on that, sure enough water coming out like a garden sprinkler. I phoned Grant technical support, explained the problem, and the chap said why don't you get it welded then ?

I got a local agricultural metal fab company to do a belt and braces job. This was clean and over weld the leaking part, then weld in a circle of steel over the dimple. Then a dd a full size metal plate over the whole back of the boiler. One of the side dimples had been weeping so this got the 1st two parts of the back fix as well. Plating was all 4mm hot rolled steel, welding was superb. Finally a good coat of hammerite over the fresh metal, a good vac & clean inside, and back together. Welding & painting cost £90. Also, used new fitting, sealants, and seals, about £35.

A little fun and games getting the air out of the system, but it hold pressure good, works better than before, and touch wood has been running for about 9 months. If you are thinking of doing this it's a messy pig of a job. It's super heavy and very difficult to manouvre. You need someone who really knows how to weld, and not leave the slightest pin hole. Patience, care and a methodical approach. As and when it dies I'll call it a day and replace it and buy narrower utility units. But for now, fingers crossed, touch wood etc it's going well, and the above helped me out of a hole.

Hope this is of some help to someone.
That is fine if you are doing the work yourself....And if someone is prepared to weld it up..90 quid sounds very cheap.
For me to drain down and remove boiler. Pressure test Then take to and return from a welder. Test again afterwards,
Rebuild and fill and test. WITH NO GUARANTEE THAT THERE WILL BE NO FURTHER LEAKS . Would not make it financially viable !!

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