Central Heating Trouble

[beanebabe]

Our central heating system has a serious air lock in it. The system was cleaned and refilled recently. All the radiators have been bled several times and there appears to be no more air in them. However the boiler, or pipes above it, are making a terrible racket and the pilot light keeps going out. One solution is apparently to fit a length of hose between the hot and cold taps in the kitchen and run the cold tap to force air out. What do you do if you have a mixer tap? Is there any other way of getting the air out of the system? Help, I'm getting cold.

[buildersmate]

The person that refilled the system should have sorted this out - did the system ever work properly since this was done?
I take it you have an open-vented CH system - the type with a small overflow / refill tank in the loft?
Normally the CH pump is perfectly capable of pushing any residual air out of the system. It pushes it along to the next rad, where it rises to the top of the rad and sits there as it can't get down to the bottom again. That's when bleeding is used to get it out.
If however, the airlock is in the vicinity of the pump itself, the pump spins in fresh air and no water gets pumped around. In that case, running the CH causes what little water there is in the boiler to overheat and boil, making the dreadful noise and locking out the boiler.
Systems should be designed so this doesn't happen - but installers sometimes put pumps in the circuit in unwise places - where air can sit around the pump if the whole system is drained. Look at the pipework in the area around the pump and around the boiler - sometimes there are drain valves located. Try opening these one by one and attempt to extract air.
PS - it is just possible that your pump is knackered - just because it hums doesn't mean it is doing anything - however given the recent service work, it is most likely to be air around the pump.

[gucciman]

the solution you have described (hose between the cold and hot taps) is used to blast air locks out of the hot water not the central heating.

as builders mate says it depends on if your system has ever worked properly since it was installed? did you buy the house recently and inherit the system? has it ever worked properly? why did you have the system cleaned?

airlocks can be an absolute nightmare and can take weeks to clear. its for that reason that we try to avoid draining a system where ever possible. it could be that your system has been designed badly and is sucking in air through the open vent.

there is another way of clearing the system of air but its involves deliberately boiling the whole system and carried a risk so therefore it is not a job you should tackle yourself. you really need to call out another heating engineer, preferably one with vast experience of old style systems as a lot of the new engineers have been brought up onmainly combi boilers and dont have a good understanding of the old systems.

have a flick through the yellow pages and see if any of the heating engineers say they used to work for british gas in their advert or look for an advert where they say they specialise in airlock removal.