Hi,

I'm in the process of installing a new central heating system and in
the best tradition of diy the job has taken a "little" longer than
anticipated. With the weather getting colder and three young children
returned home after some time away having practically no hot water
(except from the electric shower!) doesn't go down too well. So I was
wondering since I have plumbed in the condensing combi (Worcester Bosch
Greenstar 28i Junior) though not completed the CH testing yet is it
possible to fire it up and operate it just in HW mode without any water
in the CH part of the system, my understanding is that it should be
possible just wanted a second opinion ?

Thanks,

mediy

In article . com,
"mediy" writes:
Hi,

I'm in the process of installing a new central heating system and in
the best tradition of diy the job has taken a "little" longer than
anticipated. With the weather getting colder and three young children
returned home after some time away having practically no hot water
(except from the electric shower!) doesn't go down too well. So I was
wondering since I have plumbed in the condensing combi (Worcester Bosch
Greenstar 28i Junior) though not completed the CH testing yet is it
possible to fire it up and operate it just in HW mode without any water
in the CH part of the system, my understanding is that it should be
possible just wanted a second opinion ?

No. It uses the central heating water internally to heat the
hot water. Some combi's also dump out excess heat to the
central heating when the demand for hot water ceases. You
could probably get away with just one radiator, or possibly
even just a loop of pipework from flow to return (but check
installation manual for minimum length -- some boilers
require a minimum volume of water in the closed loop).

--
Andrew Gabriel

On Mon, 20 Nov 2006 20:26:27 +0000, Andrew Gabriel wrote:

In article . com,
"mediy" writes:
... I have plumbed in the condensing combi (Worcester Bosch
Greenstar 28i Junior) though not completed the CH testing yet is it
possible to fire it up and operate it just in HW mode without any water
in the CH part of the system, my understanding is that it should be
possible just wanted a second opinion ?

No. It uses the central heating water internally to heat the
hot water. ... You could probably get away with just ... a loop of
pipework from flow to return

As Andrew says you need water in the system but a loop between flow and
return, pressurised and bled (via that stupid bit of ribbed rubber hose
connected to a bleed nipple inside the boiler casing grrr!). Ensure
there's no call for CH by disconnecting the bridging link on the connector
on the PCB to be sure.

Thanks for all the replies, I think I will go with the one rad option
as I can isolate it off from the rest of the system.

Does anyone know where I can get a short (1m) length of 28mm plastic
pipe, don't want to buy 10x3m lengths!

Thanks,

mediy

John Stumbles wrote:
On Mon, 20 Nov 2006 20:26:27 +0000, Andrew Gabriel wrote:

In article . com,
"mediy" writes:
... I have plumbed in the condensing combi (Worcester Bosch
Greenstar 28i Junior) though not completed the CH testing yet is it
possible to fire it up and operate it just in HW mode without any water
in the CH part of the system, my understanding is that it should be
possible just wanted a second opinion ?

No. It uses the central heating water internally to heat the
hot water. ... You could probably get away with just ... a loop of
pipework from flow to return

As Andrew says you need water in the system but a loop between flow and
return, pressurised and bled (via that stupid bit of ribbed rubber hose
connected to a bleed nipple inside the boiler casing grrr!). Ensure
there's no call for CH by disconnecting the bridging link on the connector
on the PCB to be sure.

On Tue, 21 Nov 2006 01:34:14 -0800, mediy wrote:

Does anyone know where I can get a short (1m) length of 28mm plastic
pipe, don't want to buy 10x3m lengths!

BES online or plumbers merchants

No you cant.

In message . com, mediy
writes
Hi,

I'm in the process of installing a new central heating system and in
the best tradition of diy the job has taken a "little" longer than
anticipated. With the weather getting colder and three young children
returned home after some time away having practically no hot water
(except from the electric shower!) doesn't go down too well. So I was
wondering since I have plumbed in the condensing combi (Worcester Bosch
Greenstar 28i Junior) though not completed the CH testing yet is it
possible to fire it up and operate it just in HW mode without any water
in the CH part of the system, my understanding is that it should be
possible just wanted a second opinion ?

ITYF the heat exchanger is part of the CH circuit and needs to be under
sufficient water pressure

so ...

practically ...

no

--
geoff