Extra pump in a "combi boiler" system??

Mousy

unread,

Oct 9, 2004, 4:25:22 PM10/9/04

to

Hi,

I had a Baxi105 installed in our 13 rads/4beds/2floors house.
There are two rads that had a problem beforehand with the
less powerful "back boiler" (sharing the same water feed, one rad
on 1st floor, the other on 2nd floor).

After installing the new boiler the 2 problematic rads worked for a bit,
and then gave up.
They did the same after the plumber came back and changed a section 0f 15mm
pipe with a 22mm on the downstairs floor (same room where the back boiler
used to be), saying that this is the best he could do.

Now the 2 rads get "warmish" (but I can still leave my hand on them for
quite
sometime without scorching myself) only when the boiler heating gauge is
on max,
otherwise they are pretty much cold.

Before I put my hands on the system I would like to ask some questions:

1. If the inlet pipe on the above rads is very hot, and the outlet is very
cold,
can it be only a problem of pressure in the system, or can the
radiators,
or the valves, be faulty?

2. The plumber/installer who tried to fix the problem said that the new
boiler is further away from the 2 rads than the previous boiler, and
that
as the house has all 15 mm pipes that is the best we can get. Is it not
strange that
other rads get very hot even in the rooms next door to the one with
fulty rad?

3. Is it possible to install a pump in a system with a combi boiler?
Any links, hints, etcetera? I understand that Baxi doesn't recommend
this?

Cheers

--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/

Matthew Maddock

unread,

Oct 9, 2004, 4:37:22 PM10/9/04

to

I'm not an expert, but I assume the plumber balanced the radiators
once he had completed the work?

Matt.

"Mousy" <mene...@bertinotti.it> wrote in message
news:opsfmdok...@news.philips.com...

Paul Saunders

unread,

Oct 9, 2004, 8:22:05 PM10/9/04

to

The radiators nearest the boiler will always be inclined to take the most
heat, hence the need for balancing as the other person said. In alot of
houses the effect is minimal and you often see systems that aren't balanced
but work perfectly ok. However, I think the problem is in the pipe sizing.
15mm pipe will carry a maximum of 6Kw with a maximum length of 24 metres. I
think it is crazy that in a 13 radiator system it has been installed with
this pipe size. Normally, even in small systems, 22mm pipe is used with 15mm
feeds. It's expecting too much to send this much heat down 15mm pipe. The
installer should have known better.
I've never seen 2 pumps in a system before and trying to pump the water
round faster could result in the system becoming noisy.
As the other guy said, try balancing it by shutting down the lockshield
valves on the rads closest to the boiler and keeping the ones furthest away
opened right up. To do it properly you should use clip on thermometers and
look for a temperature difference of 11deg C between the flow and return.
Hope this helps.

"Mousy" <mene...@bertinotti.it> wrote in message
news:opsfmdok...@news.philips.com...

ARWadsworth

unread,

Oct 9, 2004, 8:28:11 PM10/9/04

to

"Paul Saunders" <psau...@bernardavenue.freeserve.co.uk> wrote in message
news:ck9vbd$hf4$1...@news8.svr.pol.co.uk...

http://www.diyfaq.org.uk/plumbing/rad-balance.html

HTH

Adam

Rainbow Chaser

unread,

Oct 10, 2004, 10:30:47 AM10/10/04

to

Have you still got some old pipe and rads. in the system?

If so, has the system been flushed?

You should see the gunge that builds up in old rads.

R.C.