Hi Andy,

Can't really offer any advice, but I have a similar problem with my
heating system. I believe air is being sucked in either down the vent
pipe, or through the radiator unions when the heating zone valve
closes. I can hear sharp spurts of hissing in radiators when the
heating is on. These spurts increase when pump overrun kicks in, and
when the overrun stops.

My system has pump overrun and is S-plan, with an automatic bypass
valve to provide a pump overrun circuit.

I originally had the bypass valve set quite high. This meant the pump
had to work to open the valve. Putting a balloon on the vent pipe saw
it blow up as the pump ramped up, and dissapear down the vent as the
bypass opened (obviously held onto the balloon!).

Setting the bypass to a low pressure improved this no end with hardly
any deflection on the balloon.

Still getting air in the system, and still trying to solve the problem.

Best Regards,
Ryan East.


Andy Twose wrote:
Hi,

Having done my heating the wrong way with pumped return etc I think I
now understand pump positioning, neutral point etc.
I have re-worked the plumbing so that I have ...

1. Pumped flow
2. Vent pipe immediately on back of pump at outlet of boiler
3. Make up pipe connected via lazy U to same position as vent pipe
4. Header tank in loft approx 8' above upstairs rads, 14' or so above
pump
5. Vent is 22 mm, make up is 15 mm both longish run

Looks like this...


Vent
| Make Up
| |
| |
| |
| |
| |
---------- | |
| | | | -------- ---------
| |-----------| Pump |------| Valve |----- To rads
| | ^__| -------- | ---------
| | |
| | | ---------
| | ----| Valve |----- To DHW
| | ---------
| Boiler |
| |
| |
| |
| |-------------- Returns
| |
----------

I now get less air in the system than before (it was bad), but still
find
I am bleeding radiators. I can sometimes hear air in the system.

To my mind, lowest pressure in system would be at connection point of
vent and make up,
and that this would be approx 14' water pressure (height of header to
downstairs).
All other points in system would be at pressures greater then this
when
pump is on.

I believe (from watching an open bleed valve on an upstairs rad) that
system goes briefly negative when heating valve closes.

Any thoughts, observations, opinions appreciated.

Andy

You can also get air entering the system if there is a leak of water
from the system. The fresh water enters via the ball valve and it
contains dissolved air which bubbles out inside the system when the
water is heated.

Robert

wrote in message
oups.com...
Hi Andy,

Can't really offer any advice, but I have a similar problem with my
heating system. I believe air is being sucked in either down the vent
pipe, or through the radiator unions when the heating zone valve
closes. I can hear sharp spurts of hissing in radiators when the
heating is on. These spurts increase when pump overrun kicks in, and
when the overrun stops.

My system has pump overrun and is S-plan, with an automatic bypass
valve to provide a pump overrun circuit.

I originally had the bypass valve set quite high. This meant the pump
had to work to open the valve. Putting a balloon on the vent pipe saw
it blow up as the pump ramped up, and dissapear down the vent as the
bypass opened (obviously held onto the balloon!).

Setting the bypass to a low pressure improved this no end with hardly
any deflection on the balloon.

Still getting air in the system, and still trying to solve the problem.

Best Regards,
Ryan East.


Andy Twose wrote:
Hi,

Having done my heating the wrong way with pumped return etc I think I
now understand pump positioning, neutral point etc.
I have re-worked the plumbing so that I have ...

1. Pumped flow
2. Vent pipe immediately on back of pump at outlet of boiler
3. Make up pipe connected via lazy U to same position as vent pipe
4. Header tank in loft approx 8' above upstairs rads, 14' or so above
pump
5. Vent is 22 mm, make up is 15 mm both longish run

Looks like this...


Vent
| Make Up
| |
| |
| |
| |
| |
---------- | |
| | | | -------- ---------
| |-----------| Pump |------| Valve |----- To rads
| | ^__| -------- | ---------
| | |
| | | ---------
| | ----| Valve |----- To DHW
| | ---------
| Boiler |
| |
| |
| |
| |-------------- Returns
| |
----------

I now get less air in the system than before (it was bad), but still
find
I am bleeding radiators. I can sometimes hear air in the system.

To my mind, lowest pressure in system would be at connection point of
vent and make up,
and that this would be approx 14' water pressure (height of header to
downstairs).
All other points in system would be at pressures greater then this
when
pump is on.

I believe (from watching an open bleed valve on an upstairs rad) that
system goes briefly negative when heating valve closes.

Any thoughts, observations, opinions appreciated.

Andy


Could be Hydrogen - not air - that's the conclusion of the BG engineer that
checked my system when I grumbled about having to bleed rads regularly.

Regards
Pete
www.thecanalshop.com

I believe (from watching an open bleed valve on an upstairs rad) that
system goes briefly negative when heating valve closes.

Any thoughts, observations, opinions appreciated.

Have you watched the overflow into the header tank when the pump
switches off? On mine I was getting a surge when the pump turned off.
Momentum of the water and/or air in the rads being compressed by the
pump then kicking back. Bleeding everything helped but didn't stop
it. Lower speed on pump also helped (but then C drop was too much so
it had to go back up). I raised the overflow pipe as far as possible.
Now the water sloshes up the pipe but doesn't go over.

Water constantly circulating into the feed tank will introduce air in
the system of course.


--

Malcolm

Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK
, or ).
Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power
electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see:

http://www.fullcircuit.com or http://www.fullcircuit.co.uk

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