Converting close coupled to combined feed & vent

[nairb999]

I have for sometime now been experiencing air problems as per this previous post

I have a Potterton Prima 60F Central Heating system - simple heating system with 16 rads each with TVR so no room stat. Had problems with air in the system for a number of years. Changed the pump approx 6 months ago and since then get a kettling noise above the pump in the feed/expansion area after the system has been running for a couple of hours. I had been advised to check for blockages by placing a magnet on the suspected pipes and the magnet was attracted to the pipe in a number of spots

Added Sentinol X400 and the system ran a lot quieter with minimal air getting into the system. So I thought the X400 had cleared the problem. After flushing the system clean - and it was thoroughly flushed through the system ran well for several hours before the kettling reappeared. The kettling noise reduces when raising the pump speed to 3.

The magnet was still attracted to the same areas of pipe and so I cut out the suspect areas. The 15mm feed pipe was partially blocked in a t piece before the pump. I have replaced this with 22mm pipe thinking that would help after talking to the pump manufacturer - Circulating pumps.

I refilled the system and as normal took me ages to get all the air out of the system. After 48 hours I was pretty sure that all was well as I ran the pump with boiler off and no gurgling noises - the pump ran very quietly with a normal water flow noise in the pipes around the pump.

When I turned the boiler back on the flow noise gradually became noisier when the boiler was firing ie on it's heat cycle. I would not call it kettling more like running water mixed with air. After 4 hours this changed on the heat cycle to more like kettling for 20 seconds then died away as the boiler turned off getting up to heat

One of the suggestions came from gas4you

Perhaps the pipe work vent/feed pipes are incorrectly installed/positioned?

Go into loft and plave a jam jar with water in it over the vent pipe. Get someone to turn on ch and see if water is sucked out of jar into vent?

If so this could be where the air is entering the system.

You could always fit a Myson aerjec where you feed/vent pipes join etc.
__________________
Dave

This test revealed water being sucked up the jar for 1 second and then falling back inot the jar followed by a number of bubbles then the level stayed steady. When I pressed my hand tightly to the bottom of the vent pipe and got my wife to turn the pump on - no noises. Therefore I think my nest step should be to go to combined feed and vent

My system is closely couple as indicated in the following photos

http://i3.photobucket.com/albums/y66/cragga_lfc/dad/CentralHeating004.jpg

This picture is showing left riser from Boiler - top left going to vent - top right cold feed and bottom right into pump ( arrow on the pump pointing down

http://i3.photobucket.com/albums/y66/cragga_lfc/dad/CentralHeating005.jpg

This picture is showing pipes going to the loft where the feed/expansion tank is directly above

On referring to the Potterton Installation & Servicing instructions it suggests an open vented fully pumped system to be fitted with a combined feed & vent.

Could I just remove the vent pipe ie replace left t by dismatling compression fittings above and below and to the right and replace with inverted L ?

 

[cowley]

The first picture you have posted shows a conventional H system layout nothing wrong at all with it, except maybe the horizontal section is a bit high above the pump.
I wouldn't change this layout apart from maybe lowering the horizontal section, what is the distance above horizontal section to f&e cistern?.

I think you should be looking elsewhere for your problem and not thinking of changing the pipe layout.

 

[nairb999]

The first picture you have posted shows a conventional H system layout nothing wrong at all with it, except maybe the horizontal section is a bit high above the pump.
I wouldn't change this layout apart from maybe lowering the horizontal section, what is the distance above horizontal section to f&e cistern?.

I think you should be looking elsewhere for your problem and not thinking of changing the pipe layout.

142 cms

Any other thoughts ?

 

[Agile]

Advice withdrawn following the involvement of Dr Drivel !

Tony

 

[nairb999]

From what you have shown its a little unusual as it seems the feed pipe is in 22 mm.

I would expect that may have a greater propensity to perhaps suck air in than the usual 15 mm feed.

Its not a normal cure but perhaps cross coupling in 22 mm between the two pipes just below the F&E tanks might help to balance the pressures at the F&E tank.

Tony

Tony - the feed pipe was originaly 15mm but I was advised to replace it with 22mm when I cut out a minor blockage in the feed pipe.

When you suggest running a 22mm just below the F&E tank would that run in parallel with the horizontal pipe 14" above the pump

 

[cowley]

The distance from the junction of the tee/ horizontal section to the f&e cistern should be okay but the more distance you have the better, i would suggest tha you move that horizontal section down to just above the pump, this will also give you an chance to see the condition of the pipework in this area.
The only part of the system which is open to the atmosphere is the open vent which goes above the f&e, you would need to draw air down to that horizontal junction to get it in your system, (if your system is'nt pumping over)IMHO to cut a tee in where suggested would make it worse.

 

[nairb999]

The distance from the junction of the tee/ horizontal section to the f&e cistern should be okay but the more distance you have the better, i would suggest tha you move that horizontal section down to just above the pump, this will also give you an chance to see the condition of the pipework in this area.
The only part of the system which is open to the atmosphere is the open vent which goes above the f&e, you would need to draw air down to that horizontal junction to get it in your system, (if your system is'nt pumping over)IMHO to cut a tee in where suggested would make it worse.

Thanks again for the feedback. When I did the jam jar test and water was sucked up the pipe briefly is that normal. I interpreted that as being drawn down to the horizontal section.

I have done some more tests which could assit proper diagnosis

I got my wife to cycle the pump on and off a number of times
with boiler stat off whilst I was in the airing cupboard. On start up gurgling noises in vent pipe and on shutting down similar noise in the feed pipe - we think cetainlty came from different areas. I then went into the loft and got my wife to repeat but I held my palm under the vent tightly to try and make a temporary block. No noise at all as she turned the pump on and off cycling every 5 seconds or so. Could that assist at all !!!!!!!!!

 

[cowley]

I assume you have a variable speed pump what setting are you using?.
High sped No3 maybe to high a setting if your system is getting a bit sludged up try lower setting No2 say to see what if any the difference is.
There is an surge in pressure at start up of pump that is why a system is designed to cater for this, but this will change as the system sludges up.

 

[nairb999]

I assume you have a variable speed pump what setting are you using?.
High sped No3 maybe to high a setting if your system is getting a bit sludged up try lower setting No2 say to see what if any the difference is.
There is an surge in pressure at start up of pump that is why a system is designed to cater for this, but this will change as the system sludges up.

Have it set on lowest setting for the last few days and that has reduced the noise.

Had the pump running for several hours and not a murmur when the boiler is off but when I switch the boiler on the running water noise sound gets greater after half an hour and then when the system is at full heat it starts sizzling. This greatly reduces when the boiler goes off and the whole cycle continues

 

[cowley]

There are products on the market to reduce system noise such as system hush, which you could try but i think you would be better off getting your system cleaned out, you say you have trv's on your radiators, have you got a bypass or at least one radiator without trv fitted in case they should all close at the same time, also what is the fitting on the horizontal pipe?.

 

[nairb999]

There are products on the market to reduce system noise such as system hush, which you could try but i think you would be better off getting your system cleaned out, you say you have trv's on your radiators, have you got a bypass or at least one radiator without trv fitted in case they should all close at the same time, also what is the fitting on the horizontal pipe?.

Cowley - thanks for your continued help. I have already cleaned the system out and the expansion tank is very clean.

A radiator in a first floor bathroom has 2 myson standard valves

The fitting on the horizontal pipe is a compression joint. I decided to use the compression joints in case I had to pull it apart again

 

[jontheplum]

in your picture is the unpainted 22mm the feed you replaced

 

[nairb999]

in your picture is the unpainted 22mm the feed you replaced

yes

 

[jontheplum]

are my eyes decieving me or is that a reducing straight connector at the top

 

[nairb999]

are my eyes decieving me or is that a reducing straight connector at the top

It is . It was easier to connect to original 15mm pipe from expansion tank. 15mm pipe is about 12" long. Is that a problem ?