I inclined the run of the vent myself as it was laid flat and I wanted to get the maximum heigth at the highest point. But the feed is still pretty much perfectly horizontal (given that the roof joists are on the level). Both pipes also have a short run at 90 deg. before they go down to the pump area. This is also horizontal. I see your point, and will try to rectify - thanks!
Has our plumber put us in danger?
- Thread starter vexation
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I inclined the run of the vent myself as it was laid flat and I wanted to get the maximum heigth at the highest point. But the feed is still pretty much perfectly horizontal (given that the roof joists are on the level). Both pipes also have a short run at 90 deg. before they go down to the pump area. This is also horizontal. I see your point, and will try to rectify - thanks!
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This post is fast becoming a poke and hope exercise instead of taking a proper diagnostic route.
I cannot see any reason to change ""Both pipes also have a short run at 90 deg. before they go down to the pump area. This is also horizontal. I see your point, and will try to rectify - thanks!"" the existing. Have several clients with such pipework but none have pumpover.
I cannot see any reason to change ""Both pipes also have a short run at 90 deg. before they go down to the pump area. This is also horizontal. I see your point, and will try to rectify - thanks!"" the existing. Have several clients with such pipework but none have pumpover.
As I see things there are two things you could do:
Raise the vent as high as possible in the roof. You can keep the horizontal run, and where the vent currently rises up just extend it till it hits the apex of your roof (assuming pitched roof) then a couple of elbows, or a upside down 'u' bend and back to the f+e tank. Some may call this rough, but if it cures the pump over then so what!
A longer job, but ultimately better than the first option would be to re-new the cold feed pipe in 22mm instead of 15mm. This will cure the pump over, bearing in mind that everything else is correctly piped up/configured properly in the airing cupboard.
Hope that helps.
Raise the vent as high as possible in the roof. You can keep the horizontal run, and where the vent currently rises up just extend it till it hits the apex of your roof (assuming pitched roof) then a couple of elbows, or a upside down 'u' bend and back to the f+e tank. Some may call this rough, but if it cures the pump over then so what!
A longer job, but ultimately better than the first option would be to re-new the cold feed pipe in 22mm instead of 15mm. This will cure the pump over, bearing in mind that everything else is correctly piped up/configured properly in the airing cupboard.
Hope that helps.
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I'm all for applying the grey-matter DP 
BTW thanks for all the ideas guys, this problem has hacked-off a fair number of visiting engineers already.
When we talk about "pump over" I don't think this is what we've got. The water only jets out the 22mm vent pipe when the pump stops (this isn't pump over is it?). This is why I keep talking about inertia. I see it as a mass of water moving at speed in 20 or 30m of 22mm pipework. Suddenly the pump stops and presents a restriction to that flow. The kinetic enegy of the moving water then forces it up the vent pipe and over the top of the inverted U above the F&E tank.
I wonder if the original configuration (swapped positions of feed and vent) mitigated this effect to a degree that stopped it short of getting over the U (this could be why the problem has only just shown up after the new work done)
Might raising the height of the U be all it needs, and simply be a reflection of the rather long run to and from the boiler? The air in the system could just be the repeated jetting into the F&E and wouldn't get in if it's just going up and down a tall pipe?
BTW thanks for all the ideas guys, this problem has hacked-off a fair number of visiting engineers already.
When we talk about "pump over" I don't think this is what we've got. The water only jets out the 22mm vent pipe when the pump stops (this isn't pump over is it?). This is why I keep talking about inertia. I see it as a mass of water moving at speed in 20 or 30m of 22mm pipework. Suddenly the pump stops and presents a restriction to that flow. The kinetic enegy of the moving water then forces it up the vent pipe and over the top of the inverted U above the F&E tank.
I wonder if the original configuration (swapped positions of feed and vent) mitigated this effect to a degree that stopped it short of getting over the U (this could be why the problem has only just shown up after the new work done)
Might raising the height of the U be all it needs, and simply be a reflection of the rather long run to and from the boiler? The air in the system could just be the repeated jetting into the F&E and wouldn't get in if it's just going up and down a tall pipe?
Pump over (in this case suction in the vent pipe) is caused by unequal pressures between vent and feed pipes. I would be investigating that, not take the vent to the moon and back in hope that pump over does not take place.
There was a time when boilers (like Kingfisher and Mexico) had upto 8 tappings. Often one set was used to connect to header tank and another to heat rads. Pipes to header tank were at same pressure (so no pump over). Pips to rads were at unequal pressure (created by pump) to make rads work.
One does not need a degree in rocket science to realise that vent and feed pipes are under the influence of pump pressure. What IF the feed-expansion pipe was connected to (out of sight) second pipe from left under flloor. If this were true, water lever would be pulled down by the pump to raise the water level in the header tank.
What is out of sight behind the dirt remover thing. Why does this pipe start as 22 and then become 15mm? To me the logical place to put the sediment remover would be before the boiler on the return (to catch the sediment coming out of the rads before it takes residence in the boiler). The gate valve would have been in the bin to be replaced by auto bypass.
There was a time when boilers (like Kingfisher and Mexico) had upto 8 tappings. Often one set was used to connect to header tank and another to heat rads. Pipes to header tank were at same pressure (so no pump over). Pips to rads were at unequal pressure (created by pump) to make rads work.
One does not need a degree in rocket science to realise that vent and feed pipes are under the influence of pump pressure. What IF the feed-expansion pipe was connected to (out of sight) second pipe from left under flloor. If this were true, water lever would be pulled down by the pump to raise the water level in the header tank.
What is out of sight behind the dirt remover thing. Why does this pipe start as 22 and then become 15mm? To me the logical place to put the sediment remover would be before the boiler on the return (to catch the sediment coming out of the rads before it takes residence in the boiler). The gate valve would have been in the bin to be replaced by auto bypass.
You seem to be ignoring what I pointed out some while ago!
The feed and vent connection to the system is only 150 mm or less apart on a 22 mm pipe. The pressure difference will be minimal as long as both pipes are not blocked.
Have you done the simple test of opening a drain cock and removing say 10 litres and seeing if the level in the F&E tank falls promptly in response?
Tony
Pump over would take place if the vent pipe was connected to the outlet of the pump. The vent (looking at the picture) is connected to the inlet, so is at negative pressure assuming the vent is connected elsewhere. When pump runs, it pulls down the water in the vent. When the pump stops, water rushes up the vent pipe to ‘spill over’ into the header tank before settling back at the same water level as in the header tank. Raising the height of the vent may stop the spill over, but never the drop of water level in the vent when the pump runs. It will however, introduce air into the system, should the water level drop past any branches to radiators.
This is how it goes behind the trap:
I can see how it could be neater, but could this be the cause of the water going up and out of the vent? These are the only lines to the F&E and they are (topologically at least) in the rigth places.
Unequal pressure between vent and feed pipes is what you blame, but I'm really struggling to understand what it means. The same head of water (give or take an inch) sits above the connecting points to the pump inlet. Doesn't that make the pressures equal? (despite the wobbly path).
Those are probably both good suggestions but I don't think they explain why we're getting water jetting out the vent.
Sorry, let me check if I've got your messages: you said there should be a vent each side of the 3-port. I agree of course, but that's not the cause of the problem. There's always trapped gas (air?) in the system no matter how often I manually vent it.
You also said that water can jet out of the vent when the pump stops if there's air in the system. I can always make it jet just by stopping the pump, irrespective of whether I have just bled everything I can find or not. Of course there may be air stuck in a local maxima that never gets vented, but I'm not sure this would be possible. Wouldn't such an air lock show up as some part of the system that stays cold?
The true identity of cause and effect is difficult to establish: the regular jet of water going into the F&E tank from the vent could be aerating the water, or air getting in somehow else could be causing the jet.
Ah thanks, a way to see if the feed is blocked. I will try it today!
These are only guesses as I have not been there or done any tests!
If the feed and vent are correctly connected with less than 150mm of 22 mm tube between them then under any normal situation the same pressure will be present in both pipes so no pump over can occur.
In the real world there will be some air in the system and this can become compressed by the pressure exerted by the pump. When the pump is depowered that compressed air can expand and force water up the feed and vent pipes, normally equally but if the feed was blocked then more out of the vent.
In any case the lower resistance of the vent would cause the level to rise initially faster anyway.
Other than air being compressed by the pump I dont see anything else that could cause this problem. I do have to say that I have not made any attempt to follow the rather convoluted pipework paths.
Tony
The only convolution I'm aware of is that little detour behind the dirt-trap. OK, it's not neat but I don't see how it could be a problem.
Just checked and the water in the tank doesn't hang about when I open the drain so I don't think the feed pipe is blocked.
If it is only 'pumping over' when the pump stops then raising the height of the vent will cure the problem.
If you don't have enough height in your roof to do this, then use 28mm pipe instead of 22mm on the way up to the highest point in your roof. This extra pipework will accommodate the sudden rush of water and so wont fall in the f+e tank, and thus not got re-airated.
As I have said some people on here may think this is rough, but it will cure your problem, if that is all that is wrong with your central heating.
If you don't have enough height in your roof to do this, then use 28mm pipe instead of 22mm on the way up to the highest point in your roof. This extra pipework will accommodate the sudden rush of water and so wont fall in the f+e tank, and thus not got re-airated.
As I have said some people on here may think this is rough, but it will cure your problem, if that is all that is wrong with your central heating.
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