I have a massive airlock in my heating/water system. I’ve had the pump changed (along with something else – a thermostat on the water tank I think) and had the boiler off the wall to ensure the heat exchanger is not clogged. All this was done 3 months ago and system was bled 3-4 times at the same time (to get rid of an airlock). I also had the whole system power flushed at that time.
Air lock is back unfortunately. I am now bleeding rads bottom-up every day. 99 times out of 100 there is no air in the rads. I regularly hear a crashing/banging in the system and can hear a gush of water from the overflow (?) into the header tank in the loft. Occasionally, say 20% of the time, the boiler goes to overheat. I then re-bleed the rads, shut the power to the boiler, wait 15/20 mins and restart. All then works but I will get the crash/bang.
Can anyone offer advice/help on what I should do next? The airlock resolution has cost me, so far in excess of £1300 and I can’t afford to blindly call people out anymore. I’d rather try to have lots of info/ideas so the engineer “thinks” I know a bit about this sort of thing and does not try to rip me off.
Make sure header tank has water in it, turn off system before bleeding, bleed all radiators starting with the furthest one downstairs, work your way upstairs, last one to bleed is nearest the hot water tank, bleed all radiators at the top of the rad via the bleed screw until all the air is out, when done bleed the water pump, screw on top of pump, only slightly turn it to allow any air to escape, there should also be a pipe next to the hot water cylinder just sticking in the air with a copper cap on it, release that slighty again letting any air out, check header tank still has water in it, turn on and see if that has done the trick..
I believe you have a blockage in your primary circuit almost inevitably where the cold feed from the F&E tank joins the primary. This is a classic cause and primary suspect when your system is pumping over as you have described. It should be the first thing to be checked - well OK after the circulator which should not be immediately condemned anyway.
The result of this blockage is that there is virtually no circulation in the sytsem which is why the rads are not heating up, heat does not get taken away from the boiler, the boiler stat kicks in and shuts it down. A power flush will not clear a blockage like that (which will be solid magnetite rather than sludge) and the pipework concerned has to be cut out and replaced.
If this is the case this is quite elementary and not being spotted by your "engineers" is (IMHO) totally incompetant. If I am right the £ 1,300 you have spent thus far has been a total waste of time and you may well have a case for recovering that money particularly if the "engineers" concerned came from BG or one of the Water Utilities.
Theres every chance you system is sucking air in from the expansion pipe, You can get a valve which is fitted to the expansion pipe which allows air/pressure to come out but does not take air in. There are also many factors involved EG: System age, Installation and Quality of plant.