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milan · Joined: 02 Sep 2003 Posts: 2 Location: London

I currently have a basic gravity system providing hot water and central heating but now is need of replacement. I am considering a combination boiler, however, is the increase in the heating-system pressure to mains-pressure an issue if i retain the existing pipework? Is there a way to check whether the pipework is adequate beforehand?

Any thoughts on this topic much appreciated!

AlanE · Posted: Wed Sep 03, 2003 7:51 am Post subject:

The heating system does not run at mains pressure. It is pressurised when cold to around 1 bar which will increase to around 2 bar when hot.

There is a pressure release valve fitted to the system that operates should the system pressure exceed 3 bar.

That having been said yes the pressurised system will find any weaknesses in your system. Try asking your heating engineer if he can test pressurise your existing system. Or are you intending doing the work yourself?

How old is your existing system and has it been filled with inhibiter? If so there shold be less of a risk involved.

Before deciding upon a combination boiler you need to consider property size and lifestyle. They are really only suitable for small flats etc.

Alan

milan · Joined: 02 Sep 2003 Posts: 2 Location: London

Thanks Alan.

I have had a couple of engineers round to give quotes for the work but only one has raised the heating system pressure as a potentail issue with respect to leaks. The current system is filled with an inhibiter and the pipe work is about 15yrs old.

What kind of pressure would an open-vented system be under when hot?

Rgds

AlanE · Posted: Thu Sep 04, 2003 7:06 am Post subject:

For all intents & purposes the same as when cold.

Pressure in a sealed system rises because as it expands when heated it is contained within a closed loop whereas with an open vented system the expanded water is passed to the Feed & Expansion tank in the loft.

Actual pressure in the system is a direct relation to the height of the tank. Therefore the pressure present in the downstairs rads would be higher than the upstairs ones.

Alan

thescruff · Moderator Joined: 03 May 2003 Posts: 4632 Location: Bath

On a half decent system the pressure would not be a problem.

Consideration should be given to changing the radiator valves as these will be worn and almost certain to leak.

An essential power flush may also cause problems by disturbing sludge and corrosion in the radiators.

The engineer who brought your attention to the posibility of having problems would get my vote.

Ask for his Corgi card and understand the areas he is qualified to work and if in doubt ask or check with Corgi online.

scruff. Cool