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
--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

"David WE Roberts" wrote in message
...
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?

My old boiler needs 2.5 metre of 22 mm pipe for the overrun bypass.

I would run the main loop to where its sensible to tap off to the rads.
Install tees with full bore isolators so you can just connect the rads up as
you install them.

On 25/07/2012 13:10, David WE Roberts wrote:
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


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.

On 25/07/12 13:10, David WE Roberts wrote:
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?

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 cock in it pointing upwards
(making it the highest point). I used the drain cock 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).

On 25/07/2012 13:10, David WE Roberts wrote:
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

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" wrote in message
...
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?


Thanks to all who responded :-)

--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")