System to Combi Boiler - Leakage worry

First-time-buyer · 30 Jun 2015

A question of the unknown really, a System Boiler which is being swapped to a Combi. The plumber has commented that a Combi being pressurised, may find weaknesses in the plumbing and pin-hole the pipes.

If this happens, the work is of course extra to rectify.

Is this something that is common, or am I worrying about nothing? The price to have the boiler changed is within budget, however spending another £1k fault finding isn't...

Newboy · 30 Jun 2015

Impossible to say - it depends on the age and condition of your existing system.

If you can't afford the possibility of having to have more work done then I'd avoid starting off the process.

Madrab · 1 Jul 2015

Could you get the system pressure tested prior to the major work being done? Hmmm... now there's a thought

ScottishGasMan · 1 Jul 2015

Problem with pressure testing is that it may not show up leaks right now, but a few heating and cooling cycles once pressurised might well spring something.

I agree it's a case of if you can't afford the whole lot then don't start.

I will however point out it is reasonably rare to have problems but your plumber is wise to advise on the possibility beforehand.

The other option is to use a plate heat exchanger. Essentially pressurising the new boiler and plate, while keeping the rest of the system under the normal pressure of the tanks. Would only cost maybe £200 more, would garuntee no extra pressure on system while still using the new pressurised boiler, with the advantage of never getting dirt from the aged system into the boiler.

Madrab · 1 Jul 2015

That could be said of any pipework though, new or old, hence the pressure testing. It's not foolproof though and it's always better to caveat any installation where older pipework is to be used.
Tis common practice, a frequent disclaimer is when I'm drilling tiles.

Pressure testing is always a best endeavours exercise but I would like to suggest that it is a recognised standard and could highlight any weaknesses.

Razor900 · 1 Jul 2015

Is it an open vented boiler with a header tank in the loft?

You said it was a system boiler, that would mean your system is already sealed so a combi would make no difference..........

Makes, models and pictures might help

polesapart · 1 Jul 2015

It's happened to me twice, that the domestic hot water pipework was OK under gravity but not under mains pressure, post combi.
Chances are that it'll be fine but installer wise to cover his arris.
Pressure test good option, IMO.

muggles · 1 Jul 2015

Alternatively, have an Intergas fitted, then you will have a combi that doesn't need the heating system to be pressurised

JimCrow · 1 Jul 2015

Razor900 said:
You said it was a system boiler, that would mean your system is already sealed so a combi would make no difference..........

.....and the hot and cold Razor

First-time-buyer · 2 Jul 2015

Hi all,

Old Ideal Mexico RS30 - Heat Only, Water Tanks in the airing cupboard etc.

Upstairs Rads - Piped under the floor
Downstairs Rads - Piped through the concrete floor.

I guess it is what is it, and the loss of pressure in the combi indicates a leak, and it would help running new drops for the new rads from the ceilings. I assume the leak can only happen on the heating side, as the heating will be at 1.5 bar (21 psi ishy). What pressure would a gravity system have, with a pump?

I could imagine a cheap installation (£1900) then another £500-£600 chasing leaks..

muggles · 2 Jul 2015

First-time-buyer said:
Hi all,

Old Ideal Mexico RS30 - Heat Only, Water Tanks in the airing cupboard etc.

Upstairs Rads - Piped under the floor
Downstairs Rads - Piped through the concrete floor.

I guess it is what is it, and the loss of pressure in the combi indicates a leak, and it would help running new drops for the new rads from the ceilings. I assume the leak can only happen on the heating side, as the heating will be at 1.5 bar (21 psi ishy). What pressure would a gravity system have, with a pump?

I could imagine a cheap installation (£1900) then another £500-£600 chasing leaks..

Don't forget with a combi your hot water pipework to your taps will also increase in pressure, so you could have a leak there too

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System to Combi Boiler - Leakage worry

Newboy

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