Thanks Azazel. I've got plenty of height available. I suppose this is one way to test the theory that it's the regular discharge from the vent into the F+E that's aerating the water. If air continues to build up in the system then at least I can rule this out. I was thinking of rigging up a temporary extension using some clear plastic tubing to see what comes through - but B&Q want an arm and a leg for the stuff.
Has our plumber put us in danger?
- Thread starter vexation
- Start date
Thanks Azazel. I've got plenty of height available. I suppose this is one way to test the theory that it's the regular discharge from the vent into the F+E that's aerating the water. If air continues to build up in the system then at least I can rule this out. I was thinking of rigging up a temporary extension using some clear plastic tubing to see what comes through - but B&Q want an arm and a leg for the stuff.
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The pump head is irrelevant here. The reason why water flows in a circuit is due to higher pressure on the outlet and lower pressure on the inlet of the pump. This is what moves the water through the pipes.
Fill a large container with water and offer this to the vent where it discharges into cistern. Get someone to switch on the system (pump runs). If my theory is correct, the vent will drink water from the container.
As I have already suggested, air ingress could well be due to dipping of water level in the vent. If vent is emptied to tee below the pump, sucked air will then be distributed to all rads.
Tony your theory might well be relevant when pressures are high (like mains pressure and dead legs) but find it hard to accept 6m head pump compressing stray air pockets to lift water by a more than 170cc assuming the vent is 700mm above cistern water level.
Fill a large container with water and offer this to the vent where it discharges into cistern. Get someone to switch on the system (pump runs). If my theory is correct, the vent will drink water from the container.
As I have already suggested, air ingress could well be due to dipping of water level in the vent. If vent is emptied to tee below the pump, sucked air will then be distributed to all rads.
Tony your theory might well be relevant when pressures are high (like mains pressure and dead legs) but find it hard to accept 6m head pump compressing stray air pockets to lift water by a more than 170cc assuming the vent is 700mm above cistern water level.
Danny, if it was 170 cc of water being expanded then in a 22 mm pipe that would raise the level about450 mm!
I am not sure where you calculated the 170 cc from. Many rads have about 1 litre of air left in the top because their bleed points are well down from the top! That air is compressed by the water pressure and over time will dissolve in the water, oxygen within a few days, nitrogen much slower.
Tony
I am not sure where you calculated the 170 cc from. Many rads have about 1 litre of air left in the top because their bleed points are well down from the top! That air is compressed by the water pressure and over time will dissolve in the water, oxygen within a few days, nitrogen much slower.
Tony
Is there a clear view of the cold feed and vent pipe along its full length?
The engineer hasn't got the 2 mixed up and accidentally swapped them around the wrong way thinking he was correcting them?
What other work was carried out other than changing the boiler itself?
Sam
The engineer hasn't got the 2 mixed up and accidentally swapped them around the wrong way thinking he was correcting them?
What other work was carried out other than changing the boiler itself?
Sam
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After a week's break, I'm back to find the top one-third of the heated towel rail full of air. I say air because I tried a flame test - and the maximum entertainment I could get was for the match to be blown out.
I find this really hard to imagine as there's a whole head of water still sitting in the F+E tank while this is going on. How could the suction empty the vent yet not noticeably effect the level in the tank? Admittedly the feed is in 15mm pipe not 22mm like the vent, but it's not blocked from what I can tell and it tees-in right next to the vent.
OK, theory confirmed: It will swallow a whole 500ml jar-full and then some.
Air *is* getting in, and the vent definitely sucks (!) but is the vent emptied to the point where air gets in at the T below the pump?DP said:
I find this really hard to imagine as there's a whole head of water still sitting in the F+E tank while this is going on. How could the suction empty the vent yet not noticeably effect the level in the tank? Admittedly the feed is in 15mm pipe not 22mm like the vent, but it's not blocked from what I can tell and it tees-in right next to the vent.
To test this I monitored the jet of water from the vent on stopping the pump before and after I vented all the air that filled the top of the towel rail (no other rads had any appreciable air in them). It made no difference that I could see.DP said:
Hi Sam. We've followed the vent and feeds carefully all the way from the pump to the tank and they're not muddled. Other than the boiler change, and the addition of a dirt-trap, the only bit of "plumbing" was switching the feed and vent as they were in the "wrong" order before.
This is the picture I posted before of where the feed pipe goes behind the trap:
You can see that the feed now comes in above the vent. It used to go straight down and into a 90' bend and reducer to the lower pipe. I don't know why it had to have a kink in it to get into the upper pipe.
When was the boiler installed? In a post you have said its an Ultimate 80FF
Hello again heatingman. This topic has gone on a bit I know, but on page one I said "the new boiler is a Glow Worm Flexicom 30hx. The old one was a Glow Worm Ultimate 80FF".
The electronic control unit in the Ultimate was failing and the old pump bearings were worn. Apart from that the system was reasonably serviceable despite having the feed and vent pipes in the "wrong" order. But now it's all been "fixed" water squirts out the vent into the header tank whenever the pump stops, the tank overflows a bit every day (still not figured out when, but splashes are left on a window below the overflow) and air can be heard circulating in the rads and pipework despite daily bleeding.
22mm cold feed &/or surge arrestor will fix it.
Agile said:
Won't the surge still push hot water up into the tank/draw water back down and aerate it in the process? Preventing the surge with a "Surge arrestor" sounds less like a palliative and more like a cure to me.
Edit: I can find plenty of electrical surge arrestors but haven't found anything that's plumbing related.
The visiting engineer today agreed with you Agile and combined the feed with the vent...
The old 15mm feed was cut and capped just before it went into the bottom of the tank, and the 22mm vent (and newly combined feed) is now T'd off in 15mm to the bottom of the tank.
Now when the pump stops the level briefly rises in the tank, and falls when it starts again. On the maximum speed setting of the pump it also jets out a little bit from the vent which he left as it was - looped over the tank.
On stopping and starting the pump you can still hear a great deal of guzzling sounds (I'm wondering what goes on in the capped-off 15mm feed) but it doesn't seem to pull air back into the system like it did before. Only just finished tho, so I'm not sure if it's really cured anything or not. After a day or so I should be able to judge it by the amount of air that ends up in the towel-rail.
The old 15mm feed was cut and capped just before it went into the bottom of the tank, and the 22mm vent (and newly combined feed) is now T'd off in 15mm to the bottom of the tank.
Now when the pump stops the level briefly rises in the tank, and falls when it starts again. On the maximum speed setting of the pump it also jets out a little bit from the vent which he left as it was - looped over the tank.
On stopping and starting the pump you can still hear a great deal of guzzling sounds (I'm wondering what goes on in the capped-off 15mm feed) but it doesn't seem to pull air back into the system like it did before. Only just finished tho, so I'm not sure if it's really cured anything or not. After a day or so I should be able to judge it by the amount of air that ends up in the towel-rail.
personally i don't like combined cf & ov.
in problem circumstances like yours i would advocate 22mm cf & ov close coupled before the pump as yours was.
with a surge arrestor fitted on the ov. basically this is a short (18" roughly) section of as large a diameter pipe as you can find set into the ov at the height of the f/e tank. the extra volume of water in this section of pipework will accommodate any water surges.
the only relevant diagram i can find is here. panel 4. 'Low Head Installations'.
http://www.idealboilers.com/docs/html/classic_se_ff_manual.html
& i don't like to run the cf like that.
in problem circumstances like yours i would advocate 22mm cf & ov close coupled before the pump as yours was.
with a surge arrestor fitted on the ov. basically this is a short (18" roughly) section of as large a diameter pipe as you can find set into the ov at the height of the f/e tank. the extra volume of water in this section of pipework will accommodate any water surges.
the only relevant diagram i can find is here. panel 4. 'Low Head Installations'.
http://www.idealboilers.com/docs/html/classic_se_ff_manual.html
& i don't like to run the cf like that.
Here tiz,
This is obviously a "done thing" then - although quite what I'd use as the surge arrester vessel is a bit of a head-scratcher (unless I use another well insulated F+E tank!)
I'm already beginning to notice steamy hot water in the tank tonight, so the combined vent and feed is looking like a waste of energy. Frankly I don't think this latest stab in the dark is much better than the earlier attempt at dunking the vent into the tank.
Edit: Why am I even having to consider "low head installation" when I have stacks of head? One thing the engineer pointed out today is that the system is run in 28mm pipe from boiler to pump - a long run of it at that. I keep seeing this figure of 3% of total system volume in the vent pipe - I bet we've got nothing like that. Does this ring any alarm bells?
i'm carrying out a similar job tomorrow & i will use some 54mm tube & 2 54*22 reducers which just happen to have had hanging about for years.
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