Hi John On your photo of combined vent and feed. Presume connection into tank is 15mm Vent pipe is 22mm. Is the pipe going to the pump 15mm?
Dreaded air in upstairs radiators and heating is off
- Thread starter nairb999
- Start date
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The mains water to the F&E tank ballcock makeup is 15MM, with isolation valve.
The combined vent and cold feed are exactly as shown, both are 22mm.
My pump pumps into the boiler return, the boiler flowpipe goes all the way up past the F&E tank and is bent over the top of the tank (the vent), all the rads (and HW cylinder coil) are teed off this flowpipe.After passing through the rads etc the water returns to the pump suction and is again pumped through the boiler etc.
In your set up, you would cut the cold feed next to the vent on the main flowpipe to your pump and blank the stub, you would then connect in the cold feed to the existing vent as close to the F&E tank as is feasible.
The combined vent and cold feed are exactly as shown, both are 22mm.
My pump pumps into the boiler return, the boiler flowpipe goes all the way up past the F&E tank and is bent over the top of the tank (the vent), all the rads (and HW cylinder coil) are teed off this flowpipe.After passing through the rads etc the water returns to the pump suction and is again pumped through the boiler etc.
In your set up, you would cut the cold feed next to the vent on the main flowpipe to your pump and blank the stub, you would then connect in the cold feed to the existing vent as close to the F&E tank as is feasible.
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John many thanks yet again for your invaluable support. So in my set up I can leave the vent pipe arrangement exactly as it is now. Do I tee the flow pipe with 15mm or 22 mm pipe. It would be approximately 200 mm long at ceiling level
Yes, vent pipe as is. It would be better to use the same diameter length of feed pipe as the vent pipe diameter. You could install a manual lever valve vent on that stub, might be handy for venting when refilling system.
I would ensure, before doing any mods, that you are happy with the flow/return pipework at the boiler
I would ensure, before doing any mods, that you are happy with the flow/return pipework at the boiler
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Pretty confident that Boiler is correctly piped. Can only be a problem if previous boiler was incorrectly piped.
I am getting the engineer back to sort the issue. I just want to ensure he has as much info as possible to come up with the right solution.
Attached is the page from Baxi manual showing 3 potential arrangements for pipe work. Any thoughts on their air separator recommendation for combined feed and vent.
I am getting the engineer back to sort the issue. I just want to ensure he has as much info as possible to come up with the right solution.
Attached is the page from Baxi manual showing 3 potential arrangements for pipe work. Any thoughts on their air separator recommendation for combined feed and vent.
Personally I prefer separate feed and vent, but I believe you can have combined with just pipework, no need for a separator.
Yes, I would agree even though mine and dozens of other people in this housing estate have never had the slithest problem with our set up, some have never added a single drop of inhibitor in those 50 years. My theory, for what its worth, about the H system is that it acts as a U tube but the surface area of the F&E tank is hundred of times that of the vent pipe area so the very very tiny differential pressure between the vent & feed tends to cause a seesaw effect when pump is running, but then again some of these systems work perfectly well?
Yes, with the H system, when the pump starts the level in the vent pipe rises slightly above the F/E tank level, hence the 150mm maximum separation to keep the rise (and potential overpumping) small. As I'm sure you know, up to about the 1970s it was normal to have the cold feed to the boiler return, giving a substantial fall in level in the vent pipe, equal to the boiler + p/w headloss. So much seesawing and ingress of aerated water, not good.
John as my cold feed is 15mm would it work to t that short piece of pipe to the vent pipe
It might, you can try it, if it doesn't you can stick in the 22mm piece, especially if doing it yourself. I'm allways mindfull of this U tube effect but probably doesn't exist with this proposed set up?.
You could just cut the cold feed high up but below the F&E tank water level and put a lever valve on the top of the pipe, vent any air (leave it cracked open) when refilling, it can then be reinstated if required or cut off low down, permanently if mods successful.
You could just cut the cold feed high up but below the F&E tank water level and put a lever valve on the top of the pipe, vent any air (leave it cracked open) when refilling, it can then be reinstated if required or cut off low down, permanently if mods successful.
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Have copied a few of the salient points from both threads and what strikes me is that there has been NO actual pump over from the vent, the "seesawing" at pump start is probably normal for this H arrangement, but shouldn't result in air ingress, so just wonder are we looking in the wrong place for the problem, maybe remake the pump flange gaskets (in rubber) as suggested by one poster.
The system with the new boiler ran for 2 months with minimal air ingress in one rad so why has air reappeared after the summer?
The system also had to backfed to refill after boiler change, bit strange? with H system where the air can escape up the vent while refilling, but this should be carried out slowly.
Its 10 years since the "H" was cut out for inspection, despite no magnetite pick up, maybe worth another visit, there's a compression coupling on the vent down low, maybe just break this and have a look/poke around inside the H.
Maybe isolate the new rad for awhile in case its causing some chemical reaction since it probably wasnt flushed through before installation, test the "air" in case its hydrogen, should light up!!.
"Recently replaced my 25year old Potterton Prima F boiler with a heat only Baxi 619 Heat. From day 1 had air in upstairs radiators.
they had a hell of a time trying to fill the system due to airlocks and the boiler kept tripping out. Eventually backfilled the system and after bleeding radiators all heated up satisfactorily.
Tested with a magnet. No issues
The previous boiler worked fine for 25 years. Boiler vent feed pump set up
The new rad should have been flushed out before installing but often isn't so don't know if this would really cause those "air" problems.
No hot water system. Separate gas water heater.
The boiler was replaced in February. It is a Baxi 619 heat only boiler. No radiators replaced. Wilo Stratos Pico 1-6. On start up suction is felt on the feed pipe for a few seconds. No suction on vent pipe. When turn the heating off no action on the feed pipe and a little air comes out of the vent pipe. This boiler is a condensing boiler and has replaced a Potterton Prima F60 which had no air issues. In the 2 months the boiler ran before shutting down for summer did get air in 1 rad in the bathroom highest point.
Another bit of information which could negate potential blockage. Have tried the magnet test on all pipes in that area and no pull detected. I did this test 10 years ago and had several areas to replace
The expansion tank is approximately 2m above the pump. The water level in the expansion tank is 2inches above feed pipe.
No harm to have it a bit higher, say maybe 6" above the feed pipe while allowing enough room for the expansion vol when the system heats up which even if your system is 100 litres will still only be ~ 2 litres or so."
The system with the new boiler ran for 2 months with minimal air ingress in one rad so why has air reappeared after the summer?
The system also had to backfed to refill after boiler change, bit strange? with H system where the air can escape up the vent while refilling, but this should be carried out slowly.
Its 10 years since the "H" was cut out for inspection, despite no magnetite pick up, maybe worth another visit, there's a compression coupling on the vent down low, maybe just break this and have a look/poke around inside the H.
Maybe isolate the new rad for awhile in case its causing some chemical reaction since it probably wasnt flushed through before installation, test the "air" in case its hydrogen, should light up!!.
"Recently replaced my 25year old Potterton Prima F boiler with a heat only Baxi 619 Heat. From day 1 had air in upstairs radiators.
they had a hell of a time trying to fill the system due to airlocks and the boiler kept tripping out. Eventually backfilled the system and after bleeding radiators all heated up satisfactorily.
Tested with a magnet. No issues
The previous boiler worked fine for 25 years. Boiler vent feed pump set up
The new rad should have been flushed out before installing but often isn't so don't know if this would really cause those "air" problems.
No hot water system. Separate gas water heater.
The boiler was replaced in February. It is a Baxi 619 heat only boiler. No radiators replaced. Wilo Stratos Pico 1-6. On start up suction is felt on the feed pipe for a few seconds. No suction on vent pipe. When turn the heating off no action on the feed pipe and a little air comes out of the vent pipe. This boiler is a condensing boiler and has replaced a Potterton Prima F60 which had no air issues. In the 2 months the boiler ran before shutting down for summer did get air in 1 rad in the bathroom highest point.
Another bit of information which could negate potential blockage. Have tried the magnet test on all pipes in that area and no pull detected. I did this test 10 years ago and had several areas to replace
The expansion tank is approximately 2m above the pump. The water level in the expansion tank is 2inches above feed pipe.
No harm to have it a bit higher, say maybe 6" above the feed pipe while allowing enough room for the expansion vol when the system heats up which even if your system is 100 litres will still only be ~ 2 litres or so."
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John your continual support is most appreciated. Just one extra piece of information I have not replaced a radiator.
A little more detail on previous boiler did have air ingress on that system and that's why the H was modified and that did not have any effect so my hesitancy on changing to combined vent and feed. Eventually on the previous boiler managed to remedy air ingress by balancing the radiators. Could that have been by chance?
I say that because everybody says balancing would have no effect. Although the system ran for 10 years with no issues.
Coming back to present arrangement it is very noticeable the suction on start up on the feed pipe for 20 secs and on the vent pipe for 1 or 2 secs.
The orifice that is connected to the feed pipe is 10mm diameter at most so why is 22 mm pipe required.
Just a thought on the air in more radiators now. Could that be because I am circulating cold water and not hot.
I am an electrical engineer with limited knowledge of central heating systems so please forgive me if I ask strange questions.
Kind regards
Brian
A little more detail on previous boiler did have air ingress on that system and that's why the H was modified and that did not have any effect so my hesitancy on changing to combined vent and feed. Eventually on the previous boiler managed to remedy air ingress by balancing the radiators. Could that have been by chance?
I say that because everybody says balancing would have no effect. Although the system ran for 10 years with no issues.
Coming back to present arrangement it is very noticeable the suction on start up on the feed pipe for 20 secs and on the vent pipe for 1 or 2 secs.
The orifice that is connected to the feed pipe is 10mm diameter at most so why is 22 mm pipe required.
Just a thought on the air in more radiators now. Could that be because I am circulating cold water and not hot.
I am an electrical engineer with limited knowledge of central heating systems so please forgive me if I ask strange questions.
Kind regards
Brian
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