We have occasional noise (gurgling, bubbling) from our hot water system when the boiler kicks in. Two automatic air vents seem to have been leaking as they are encrusted with whitish deposits.
I'd like to replace them as I understand they can get gummed up and stop working.
Are they easy to replace? If they're unscrewed, am I likely to get a soaking?
Is it correct that, once fitted, the new AAVs should have the caps shut and then opened by 1 turn?
I'd be grateful for any advice that will save me a large bill.

Roger, January 2009

Thanks JD. If I succeed with the replacement, is it normal to set them by opening them up slightly?

Roger, January 2009

well if it was me id bung the header tank, if its an open vented system, should be a small black tank in attic or highlevel somewere, if you dont have bungs then turn the valve of to the tank and drain system down, to below the level the air vents, you may have top open the motorised valves manually, to drain the system, once u repair the air vents, turn the tank back on and allow the system to fill back up, you will most likely have to bleed the radiators, let the new AAV's do there job

jazz drummer, January 2009