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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Help - Converting from "system to "combi" https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1309893133 Message started by badger007 on Jul 5^th, 2011, 8:12pm

Title: Help - Converting from "system to "combi"
Post by badger007 on Jul 5^th, 2011, 8:12pm

Help.

I'm replacing an oil fired CH system with gas. The current system is what I understand as a "system" with a small head tank in the loft. I don't know what pressure it works at but its probably low.

I'm going to get a combi boiler and I'm being advised to rip it all out and replace with plastic (not sure about that) and some are advising copper replacement throughout.

Now; I'm not a CH Engineer or a plumbler but it seems a viable option to graft new radiators onto the existing pipework provided

1) Its not clogged (its been regularly treated with fernox)
2) The joints are OK (it looks as if compression fittings have been used for joints) - Are these likely to be dodgy??
3) The system is flushed before connecting the new boiler

So, what I'm asking of someone with no axe to grind

Is it realistic to pressure test the current system (pneumatically) at gradually increasing pressure to say 4 bar to ensure the system is tight, then graft on the boiler and radiators

OR.

Should it fail, replace the joints with soldered joints and start again?

OR

Should I rip out and start afresh? Then Plastic or Copper?

Any help gratefully recieved

(Current pipework was installed in 1966)

Badger

Title: Re: Help - Converting from "system to "combi"
Post by londonman on Jul 5^th, 2011, 9:34pm

Here's my two'pennorth (although I'll admit I'm nowhere in the same league as Scruff)...

...1) how will you find the leak if the pressure test fails?

2) I do know that some combi's are perfectly happy to work as part of a system, (ie low pressure as you have now).

Title: Re: Help - Converting from "system to "combi"
Post by thescruff on Jul 6^th, 2011, 1:16am

You should never test with air.

Why not buy an Intergas boiler and connect to the existing open vent system, you shouldn't have to worry about the pressure.

And you get a good reliable boiler.