My heating and hot water system pumps over into the small tank in my
loft. I had a new pump fitted about six months ago and it was after
this that I first noticed the problem. I had the pump setting turned
down and this appeared to solve the problem only for it to return
again. It is hot water that is being pumped over for the duration of
the time that the system is on.
Yesterday I had a full power flush. The system was very dirty and the
flush has rendered the system quieter. The guy tested the system and
there was no pumping over when he was here. When the system kicked in
this morning, I went to check the tank in the loft and I was horrified
to see that the pumping over of hot water water was back.
Anyone any idea how to solve this problem?

wrote:
My heating and hot water system pumps over into the small tank in my
loft. I had a new pump fitted about six months ago and it was after
this that I first noticed the problem. I had the pump setting turned
down and this appeared to solve the problem only for it to return
again. It is hot water that is being pumped over for the duration of
the time that the system is on.
Yesterday I had a full power flush. The system was very dirty and the
flush has rendered the system quieter. The guy tested the system and
there was no pumping over when he was here. When the system kicked in
this morning, I went to check the tank in the loft and I was horrified
to see that the pumping over of hot water water was back.
Anyone any idea how to solve this problem?


This is most commonly caused by incorrect positioning of the vent pipe
branch, too close to the pump. It is rarely fixable without relocating
the vent branch further away from the pump output.


--
Grunff

"Grunff" wrote in message
...
wrote:
My heating and hot water system pumps over into the small tank in my
loft. I had a new pump fitted about six months ago and it was after
this that I first noticed the problem. I had the pump setting turned
down and this appeared to solve the problem only for it to return
again. It is hot water that is being pumped over for the duration of
the time that the system is on.
Yesterday I had a full power flush. The system was very dirty and the
flush has rendered the system quieter. The guy tested the system and
there was no pumping over when he was here. When the system kicked in
this morning, I went to check the tank in the loft and I was horrified
to see that the pumping over of hot water water was back.
Anyone any idea how to solve this problem?


This is most commonly caused by incorrect positioning of the vent pipe
branch, too close to the pump. It is rarely fixable without relocating
the vent branch further away from the pump output.

The diagrams I've seen show the poisition of the vent pipe on the input side
of the pump, so the order is
1) Flow from boiler
2) Vent pipe
3) Inlet pipe from F&E tank, no more than 150mm from vent pipe
4) Pump inlet

Is this an acceptable configuration or have I got it wrong?

PM wrote:

The diagrams I've seen show the poisition of the vent pipe on the input side
of the pump, so the order is
1) Flow from boiler
2) Vent pipe
3) Inlet pipe from F&E tank, no more than 150mm from vent pipe
4) Pump inlet

Is this an acceptable configuration or have I got it wrong?

This works well - as long as you have the feed pipe *in between* the
vent and the pump (as per your description). Placing the vent
immediately before the pump often leads to air being sucked down it,
which is as bad as pumping over.

You can get away with placing the vent on the pump outlet side, but if
you do it needs to be further away from the pump - past the radiator +
tank branch offs.


--
Grunff

Grunff wrote:

PM wrote:

The diagrams I've seen show the poisition of the vent pipe on the input side
of the pump, so the order is
1) Flow from boiler
2) Vent pipe
3) Inlet pipe from F&E tank, no more than 150mm from vent pipe
4) Pump inlet

Is this an acceptable configuration or have I got it wrong?

This works well - as long as you have the feed pipe *in between* the
vent and the pump (as per your description). Placing the vent
immediately before the pump often leads to air being sucked down it,
which is as bad as pumping over.

You can get away with placing the vent on the pump outlet side, but if
you do it needs to be further away from the pump - past the radiator +
tank branch offs.


--
Grunff

The new pump was placed in exactly the same position as the old one, ie
just above the boiler.

"Grunff" wrote in message
...
PM wrote:

The diagrams I've seen show the poisition of the vent pipe on the input
side
of the pump, so the order is
1) Flow from boiler
2) Vent pipe
3) Inlet pipe from F&E tank, no more than 150mm from vent pipe
4) Pump inlet

Is this an acceptable configuration or have I got it wrong?

This works well - as long as you have the feed pipe *in between* the
vent and the pump (as per your description). Placing the vent
immediately before the pump often leads to air being sucked down it,
which is as bad as pumping over.

You can get away with placing the vent on the pump outlet side, but if
you do it needs to be further away from the pump - past the radiator +
tank branch offs.


--
Grunff

Thanks Grunff - when the feed and vent are between the boiler and pump is it
better to have them nearer the boiler, the pump or is it immaterial? I am
about to plumb in a new boiler and can adjust to suit.

"AJH" wrote in message
...

Taller loop in the vent pipe over the feed and expansion (header)
tank?? Better still a pressurised system.


Better still just a 22mm feed rather than the combination of a vent a feed.
Far easier to fill, put in inhibitor etc than a pressurised system -
particularly if there's already the header tank etc.

(As long as the boiler is designed for a pressurised system!)

PM wrote:

Thanks Grunff - when the feed and vent are between the boiler and pump is it
better to have them nearer the boiler, the pump or is it immaterial? I am
about to plumb in a new boiler and can adjust to suit.

I think this usually gets decided based on physical pipe locations
(whatever is easiest). Logically, the closer to the boiler the better.


--
Grunff

In an earlier contribution to this discussion,
PM wrote:


When the feed and vent are between the boiler and
pump is it better to have them nearer the boiler, the pump or is it
immaterial? I am about to plumb in a new boiler and can adjust to
suit.

It doesn't really matter. The important thing is that the vent and feed
pipes must be on the *same* side of the pump, and as close together as
possible - so that the flow along the main pipe doesn't cause any
appreciable differential presssure between the vent and feed pipe connection
points.

--
Cheers,
Roger
______
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"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
PM wrote:


When the feed and vent are between the boiler and
pump is it better to have them nearer the boiler, the pump or is it
immaterial? I am about to plumb in a new boiler and can adjust to
suit.

It doesn't really matter. The important thing is that the vent and feed
pipes must be on the *same* side of the pump, and as close together as
possible - so that the flow along the main pipe doesn't cause any
appreciable differential presssure between the vent and feed pipe
connection
points.

--
Cheers,
Roger


Thanks Roger

"Grunff" wrote in message
...
PM wrote:

Thanks Grunff - when the feed and vent are between the boiler and pump
is it
better to have them nearer the boiler, the pump or is it immaterial? I
am
about to plumb in a new boiler and can adjust to suit.

I think this usually gets decided based on physical pipe locations
(whatever is easiest). Logically, the closer to the boiler the better.


--
Grunff

Thanks

Pete

On 2006-09-05 13:13:26 +0100, Grunff said:

PM wrote:

The diagrams I've seen show the poisition of the vent pipe on the input side
of the pump, so the order is
1) Flow from boiler
2) Vent pipe
3) Inlet pipe from F&E tank, no more than 150mm from vent pipe
4) Pump inlet

Is this an acceptable configuration or have I got it wrong?

This works well - as long as you have the feed pipe *in between* the
vent and the pump (as per your description). Placing the vent
immediately before the pump often leads to air being sucked down it,
which is as bad as pumping over.

You can get away with placing the vent on the pump outlet side, but if
you do it needs to be further away from the pump - past the radiator +
tank branch offs.

The order doesn't really matter.

The critical aspect is that the vent and feed pipes join the circuit as
close together as possible and certainly not with either the pump or
boiler between them.

A good way to achieve this is with an air separator like the Myson
Aerjec which apart from preventing this problem facilitates easy
venting while filling the system.