How small a CH circuit can you have? (temporarily)

[David WE Roberts]

We may be in a position where we want a new combi commisioned to supply hot water some time before we are anywhere near installing the replacement pipe runs etc. for the central heating.

Now AIUI we will need water in the CH side at about 1bar pressure otherwise the boiler won't run. We don't intend to use the heating circuit, so what is the safe minimum to allow the boiler to run? Short loop of 22mm? Single temporary radiator to give some volume so pressure doesn't fluctuate too much?

Cheers

Dave R

[Chris Bartram]

Our Alpha combi ran perfectly happily with the central heating isolators closed (i.e: no CH circuit external to the boiler) when we had a leak. YMMV.

[Cod Roe]

I had something very similar when I installed my Vaillant Ecotec Pro 28, I had enough 22mm in to go upstairs and to the point of the first T under the floor (about 3m), at which point I joined the feed and return together, and added a T piece with a drain c*ck in it pointing upwards (making it the highest point). I used the drain c*ck to vent the system when I filled it. Worked fine for the couple months till I got the rest of the central heating finished (which fortunately coincided with the beginning of winter).

[newshound]

I believe most modern combis have an internal bypass which is all they need. As for expansion / pressure fluctuations, that's what the expansion vessel is for.

But check the combi installation manual, which you can usually get off the web before you buy it.

[David WE Roberts]

Thanks to all who responded :-)