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Discuss Air in central heating system ( lots of it!) in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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Hi All
Apologies in advance for basic information and layman's knowledge.
I have a 30 year old bungalow and have been in for nearly 3 years with few problems but recently the central heating got noisier and noisier with gurgling and the radiator closest to the boiler filled with air so quickly that after a few days it was losing temperature at the top and then went cold except for the bottom couple of inches. I bled it and the header tank lowered with the float valve tied up so the system is full of water again but a few days later it was cold again and a repeat of the bleeding had the same effect. It's an oil fired boiler and unusually has two pumps one on each side of the boiler at the bottom pumping the water into the boiler. One set of pipes goes straight into the floor and to the rads and the other goes up into the loft and to the airing cupboard where it comes out of the ceiling into the cylinder. There are 2 tanks in the loft and both seem like they are both normal. The pumps are a grundfoss on the heating and a wilo on the hot water side. The worst thing now is that not only is the radiator getting full of air but the wilo pump is swishing so much that I have been switching it off as I am concerned that the boiler is getting full of air too. There are two caleffi valves in the loft on the feed and return pipes to the cylinder/boiler on stabbings a foot above the joists not far from where the pipes come up from the wilo pump. If I knock off the radiator nearest the boiler the others gurgle and go cold progressively if I close them off in turn. I assumed I had a leak because logic told me as a layman that if air was in then water has escaped and being a solid concrete floor it was losing underground but not showing damp yet on the floor and wall. Anyway, after contacting the insurance for trace and access and getting nowhere and local plumbers all suggesting different causes and solutions I am up against a wall and unsure what to do. The boiler has been serviced annually and he said it's good from a burner and control point but he thinks it's a leak that will corrode the boiler first and be very expensive so for the last few weeks I have been unwilling to run it. I have put fernox in year 1 and build base own last year because they said it's equivalent and didn't have fernox in stock and since the problem got worse I have put it in every time I bled the rads. The only thing is now I've sheared the bleed screw off the back panel of the double that gets air first so only the front has water in. I've ordered another myson identical replacement for delivery in 5/10 working days. And the final thing is that a new radiator was fitted in a utility room we've converted to an en suite but the pipes were hidden behind units and we were pleased when they were uncovered but the trv has been shut for so long it won't open but I have ordered a new one and the rad has been bled via the lockshield and it's full of water. So PLEASE if anyone can support me with advice so when the radiator comes I can fit it and fix the problems in the meantime I would really appreciate it. Thanks.
 
Just wanted to add to the first post that there are bubbles rising into the f/e tank in the loft out of the fill outlet in the base of the tank at the rate of one every 5 seconds. Also the tank didn't lose any water over several days with the ball valve tied up and the system not running and this made me think maybe there wasn't a leak as I would expect water to run out even when the pumps are not running? The level in the tank stayed within a few mom's of the original level as best as I can measure. Thanks.
 
Just wanted to add to the first post that there are bubbles rising into the f/e tank in the loft out of the fill outlet in the base of the tank at the rate of one every 5 seconds. Also the tank didn't lose any water over several days with the ball valve tied up and the system not running and this made me think maybe there wasn't a leak as I would expect water to run out even when the pumps are not running? The level in the tank stayed within a few mom's of the original level as best as I can measure. Thanks.

My first guess is that a (partial) blockage somewhere is causing air to be pulled down the vent pipe by the circulation pump. Can you provide a few photographs of the pipework, pumps, etc.?

Can you hold a mug of water (get it from the expansion tank so there is some inhibitor in it) so the end of the vent pipe dips into it? If this stops your bubbles and/or the level in the mug drops we've found where the air is getting in and the next step is to pin down why.
 
My first guess is that a (partial) blockage somewhere is causing air to be pulled down the vent pipe by the circulation pump. Can you provide a few photographs of the pipework, pumps, etc.?

Can you hold a mug of water (get it from the expansion tank so there is some inhibitor in it) so the end of the vent pipe dips into it? If this stops your bubbles and/or the level in the mug drops we've found where the air is getting in and the next step is to pin down why.
 
Hi Chuck. Thanks for your kind information, you are absolutely spot on! When I did another check it became obvious that the valve on the pipe to the coil in the cylinder (at the bottom, inlet or return, not sure) was closed or very nearly shut. When I opened it up fully there was an immediate improvement in reducing the noise in the radiators and pump on the hot water side and it's been running normally since. Thanks a bunch. I can only guess the kitchen/bathroom fitter who put the shower, basin and new radiator in the new ensuite recently ( about 6 weeks ago must have been isolating things and this was done then. So I am very happy thanks for the pointers as yes there was an obstruction in the pipes! I am surprised that air can get into a closed system to displace water without any obvious place for the water to go, that is why I assumed I had a leak. But when I think about it the level of water in the header tank was lower when I bled the radiators than it was when the rads were full of air so I guess the displacement was raising the level in the loft? Anyway I can sleep easier now and let the insurance company know it was a false diagnosis from the boiler service guy. The only thing now is that one rad is cool at the bottom and hot at the top so maybe the air has concentrated the sludge in the bottom as it was usually red hot and when the radiator is changed in the other room I will get it out and desludged, but at least I should not have to dig up the floor!!!! Thanks very much indeed.
 
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