Cannot shift CH airlock

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I have always had issues with my open-vented CH (posted here in 2009). Radiators take ages to heat up, particularly two large radiators downstairs. Eventually heat gets to them, but the return is luke warm. I suspect an airlock on the return. Boiler recycles frequently. I gravity flushed and the water was clear. I have renewed the pump. I have thoroughly mains flushed, radiator by radiator, and then all radiators together. On turning off the mains, water was still exiting the drain for a while. I closed the drain and opened the fill, and some water rushed up the fill pipe. This suggests to me that there is still a large, compressed air lock after the mains flush. (Of course, I have bled all the radiators!) Any suggestions?
 
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Fully pumped system? Boiler type? All this helps to give a better answer. Large, compressed air lock in a vented system? Don't know what you mean by that.
 
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Fully pumped system? Boiler type? All this helps to give a better answer. Large, compressed air lock in a vented system? Don't know what you mean by that.
Yes, fully pumped (brand new Wilo Yonos) system. Boiler Viessman 100C (10 years old). I think there may be air trapped in the rather long return to the boiler.
 
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X800 in and leave for a few days... Clear water does not mean there are no blockages!
 
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X800 in and leave for a few days... Clear water does not mean there are no blockages!
I also wondered if there may still be blockages, but they would have to be in most of radiators (including the two nearest the boiler upstairs). I think there is still an air lock that needs to be addressed. The reason I say this is that a) after closing the mains flush, water still came out the drain and when closing the drain and opening the fill, water went up the fill pipe, b) during operation, hot water can get pushed up the feed (even if I turn the pump down to 2), c) when the system is turned off and the pump stops, there is a gurgling of water and air. These both indicate to that there is pressure remaining in the system. Do you think I should run the X800 first and address the air lock afterwards?
 
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Short of a power flush, x800 is the best you'll be able to do to clear any sludge or concretions. Are your ground floor rads on drops?
 
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So you now questiong that the rads you mains flushed could still be blocked? Water going up the vent during operation is known as pumping over, and is most commonly caused by a blockage just upstream of the pump, where the feed and vent join the system pipe work, or sometimes by a poorly configured system.
You are making a lot of incorrect assumptions from the way your system is performing.
If you've got blockages where I've suggested you look, then chemicals will not be the answer. Have you tried a magnet on the copper pipework around the feed and vent connections?
 
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Also he seems to be assuming the system was properly balanced in the first place?
 
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Short of a power flush, x800 is the best you'll be able to do to clear any sludge or concretions. Are your ground floor rads on drops?
The system was flushed by the last plumber about 6 years ago using FX2. He did not clear it properly and I could light the 'air' coming out the bleed valve! I have a set of four rads upstairs with one on a downstairs and a set of three rads all on a downstairs drop. Two other rads upstairs connect into the last run of the return.
 
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So you now questiong that the rads you mains flushed could still be blocked? Water going up the vent during operation is known as pumping over, and is most commonly caused by a blockage just upstream of the pump, where the feed and vent join the system pipe work, or sometimes by a poorly configured system.
You are making a lot of incorrect assumptions from the way your system is performing.
If you've got blockages where I've suggested you look, then chemicals will not be the answer. Have you tried a magnet on the copper pipework around the feed and vent connections?

I go with gasman, had many like this 9 times out of 10 its a blockage, the sort a power flush and chemical wont shift, hard coke stuck in an elbow or T even a screw driver wont shift.
 
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So you now questiong that the rads you mains flushed could still be blocked? Water going up the vent during operation is known as pumping over, and is most commonly caused by a blockage just upstream of the pump, where the feed and vent join the system pipe work, or sometimes by a poorly configured system.
You are making a lot of incorrect assumptions from the way your system is performing.
If you've got blockages where I've suggested you look, then chemicals will not be the answer. Have you tried a magnet on the copper pipework around the feed and vent connections?
I mains flushed each rad in turn for several minutes and the water was clear. Even on my first gravity flush, there was no sludge or discoloration right from the start. As dilalio said, I seem to have incorrectly assumed that there was no sludge because of this. What other incorrect assumptions have I made so far?
I have tried magnets around the F&E pipework and have not noticed any attraction. I did not expect to because I used the fill to refill the system and, when hot water was going up the feed, I temporarily closed it to prove it was free to go up the expansion.
 
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So you now questiong that the rads you mains flushed could still be blocked? Water going up the vent during operation is known as pumping over, and is most commonly caused by a blockage just upstream of the pump, where the feed and vent join the system pipe work, or sometimes by a poorly configured system.
You are making a lot of incorrect assumptions from the way your system is performing.
If you've got blockages where I've suggested you look, then chemicals will not be the answer. Have you tried a magnet on the copper pipework around the feed and vent connections?

I go with gasman, had many like this 9 times out of 10 its a blockage, the sort a power flush and chemical wont shift, hard coke stuck in an elbow or T even a screw driver wont shift.
When you say 'hard coke', do you mean non-magnetic material? I have access to all the lowest pipework and angles and my magnet indicates no sign of anything magnetic there. I think a partial blockage would probably make it impossible to shift an airlock (and I do think I have one) because the flow would not be strong enough.
 
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I have tried magnets around the F&E pipework and have not noticed any attraction. I did not expect to because I used the fill to refill the system and, when hot water was going up the feed, I temporarily closed it to prove it was free to go up the expansion.
That's not a test that proves anything, other than the feed and expansion pipes are clear. I still think your problem is around your pipework upstream of the pump, and yes, this can be non magnetic. Are your motorised valves operating correctly?
 
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