I've just drilled through a pipe under the floorboards :-( It's one of
the 22mm pipes between the condensing (not combi) boiler and the hot
water cistern. I've fixed it and bled (bleeded?) the pump. The boiler
starts normally but then goes off after about a minute without heating
the water.

I'm assuming water is coming from the loft header tank because air and
then black water came out of the pump when I bled it. There isn't any
air in the upstairs radiators.

Any ideas?

On Sat, 03 May 2008 16:39:13 +0100, Another Dave wrote:

I've just drilled through a pipe under the floorboards :-( It's one of
the 22mm pipes between the condensing (not combi) boiler and the hot
water cistern. I've fixed it and bled (bleeded?) the pump. The boiler
starts normally but then goes off after about a minute without heating
the water.

I'm assuming water is coming from the loft header tank because air and
then black water came out of the pump when I bled it. There isn't any
air in the upstairs radiators.

Any ideas?

I presume this is conventional (or should I now be saying traditional?)
system with a small heating header tank in the loft.
You very like have an air lock.
This may in part be due to a blockage where the feed pipe joins the
primary circuit. If you could get a picture of the general arrangement of
the pump and pipes I might be a lot more specific.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Sat, 03 May 2008 16:39:13 +0100, Another Dave wrote:

Any ideas?

A fairly common gotcha to check is whether there's an air bleed valve at a
high point in the pipework, probably near the hot water cylinder (not
"cistern"). If this is full of air it can stop circulation.

Came across a big old system recently where a couple of rads weren't
heating up. Tracing their pipework (using my X-ray vision[1] since they
were hidden in skirting trunking) I found they were connected across the
primary coil on the HW cylinder! The pipework branching to the rads was
on a high point with an automatic air bleed valve and the branch was cold.
Percussive therapy failed to free the AAV so I loosened it to let the air
out and presto - hot rads!



--
John Stumbles

Testiculate [v.t]
To wave one's arms around while talking ********.

John Stumbles wrote:
On Sat, 03 May 2008 16:39:13 +0100, Another Dave wrote:

Any ideas?

A fairly common gotcha to check is whether there's an air bleed valve
at a high point in the pipework, probably near the hot water cylinder
(not "cistern"). If this is full of air it can stop circulation.

Came across a big old system recently where a couple of rads weren't
heating up. Tracing their pipework (using my X-ray vision[1] since
they were hidden in skirting trunking) I found they were connected
across the primary coil on the HW cylinder! The pipework branching to
the rads was on a high point with an automatic air bleed valve and
the branch was cold. Percussive therapy failed to free the AAV so I
loosened it to let the air out and presto - hot rads!

Love the sig.. Listening to Brothers in Arms whilst scanning through.

Another Dave wrote:
I've just drilled through a pipe under the floorboards :-( It's one of
the 22mm pipes between the condensing (not combi) boiler and the hot
water cistern. I've fixed it and bled (bleeded?) the pump. The boiler
starts normally but then goes off after about a minute without heating
the water.

I'm assuming water is coming from the loft header tank because air and
then black water came out of the pump when I bled it. There isn't any
air in the upstairs radiators.

Any ideas?

Strictly bodgerama, but it works for me. Turn off every rad except one
and set the boiler going. After 10 mins open another rad and shut the first
one, repeat this all over the house bleeding as you go - one open rad only.

I assume that directing the full force of the pump into one particular part
of the circuit is more effective in flushing air bubbles forward into
locations where they can be successfully bled off.

"Another Dave" wrote in message
...
I've just drilled through a pipe under the floorboards :-( It's one of
the 22mm pipes between the condensing (not combi) boiler and the hot
water cistern. I've fixed it and bled (bleeded?) the pump. The boiler
starts normally but then goes off after about a minute without heating
the water.

I'm assuming water is coming from the loft header tank because air and
then black water came out of the pump when I bled it. There isn't any
air in the upstairs radiators.

Any ideas?

Happened twice to me.
Attach a hose to the c/h overflow pipe (other end to mains water) and run
mains water through.
2 minutes and lotsa bubbles in the header tank later, problem solved.

P

On Sun, 04 May 2008 22:46:35 +0100, Peter wrote:

"Another Dave" wrote in message
...
I've just drilled through a pipe under the floorboards :-( It's one of
the 22mm pipes between the condensing (not combi) boiler and the hot
water cistern. I've fixed it and bled (bleeded?) the pump. The boiler
starts normally but then goes off after about a minute without heating
the water.

I'm assuming water is coming from the loft header tank because air and
then black water came out of the pump when I bled it. There isn't any
air in the upstairs radiators.

Any ideas?

Happened twice to me.
Attach a hose to the c/h overflow pipe (other end to mains water) and run
mains water through.
2 minutes and lotsa bubbles in the header tank later, problem solved.

I think you mean the vent, not overflow, pipe!

To be clear what the problem is, IME an airlock results in radiators not
bleeding: you can take the bleed screw right out but after a point no
more air comes out but no water comes out, so the rad(s) doesn't/don't
fill. The OP says there isn't any air in the upstairs radiators which I
assume means they've bled and are now full of water, but he's getting no
circulation.

Another thing he could check is whether there's an automatic air bleed
valve on top of, or possibly inside the boiler, and whether the cap is
loose and air hisses out when the system is filled.

--
John Stumbles

Just because you're paranoid doesn't mean they're not out to get you.

On Sun, 04 May 2008 15:00:51 +0100, Steve Walker wrote:

Another Dave wrote:
I've just drilled through a pipe under the floorboards :-( It's one of
the 22mm pipes between the condensing (not combi) boiler and the hot
water cistern. I've fixed it and bled (bleeded?) the pump. The boiler
starts normally but then goes off after about a minute without heating
the water.

I'm assuming water is coming from the loft header tank because air and
then black water came out of the pump when I bled it. There isn't any
air in the upstairs radiators.

Any ideas?

Strictly bodgerama, but it works for me. Turn off every rad except
one and set the boiler going. After 10 mins open another rad and shut
the first one, repeat this all over the house bleeding as you go - one
open rad only.

I assume that directing the full force of the pump into one particular
part of the circuit is more effective in flushing air bubbles forward
into locations where they can be successfully bled off.

This works well unless the problem is air in the pump itself.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html