Bottle Air Vent Problem

diplonics

Have a bottle air vent fitted (similar to the one at this link: http://www.comparestoreprices.co.uk/home-improvement/comap-bottle-air-vent-3-8.asp) to a sealed central heating system. It is fitted to the back of the boiler about 2 inches above it in combination with a pressure relief valve similar to this one:
http://www.plumbworld.co.uk/12-3-bar-ff-pressure-relief-231-57

My question is, does the bottle air vent have to be at the highest point in the system? or can/do they break/leak easily.

While not a plumber I have managed to maintain the sealed system myself and up to a few months ago the pressure stayed constant for months on end. However, about a year ago I added another rad to the system but it is vertical and clearly a meter or so higher than the bottle air vent. This rad can tend to collect air but after a couple of weeks bleeding it and topping up the pressure the system will settle down and the rad works fine and the pressure stays constant. I recently moved out of the house temporally but left the heating running for an hour a day. The boiler is woodpellet but if I don't get back every couple of weeks to refill the hopper or empty the ash pan the boiler will stop working, however the pump will continue to circulate water for the hour. What I've noticed is that if the boiler is not heating the water, i.e. is stopped, but the pump continues to circulate cold water that it leaks quite heavily from the plastic cap on the top of the bottle air vent. Does this sound like the bottle air vent is just broken or is it related to not being the highest point in the system anymore and pumping cold water has some affect I don't understand.

I could easily extend it higher in the boiler house to be above the vertical rad or just replace it if its broken. Any comments or advice from someone with experience would be appreciated.

Thanks.

Micky Dolenz

AAV don't have to be at the top of the system, they are usually at the top of boiler and on flow pipe at cylinder.

Sounds like you have a damaged one, it won't leak when the system is hot most probably because the hot water expands and seals the leak, it must be small.

Change the AAV, if you can it would be a good idea to put a valve under it so you won't need to drain down system if it goes again.

diplonics

Thanks for this.

Your last point is well noted and I'll do this.

items

Pretty much as Micky says, AAV located at top of boiler /cylinder coil to ensure circulation. Industrial type installations will have AAV's fitted any time pipe work rises, these systems contain a lot more water and have much longer pipe runs, domestic no real need to fit additional AAV unless a section of pipe work creates problems for entire system.

You can buy an AAV with spring loaded valve, looks the same as a 312 fitting. Soon as AAV removed spring raises and closes opening, saves from installing a valve, sometimes no room for valve but its without doubt best practice to install valve before AAV.

Before replacing, remove AAV cap and clear out any opening's with a pin / needle etc. After some time the opening becomes blocked with deposits from hard water / heating sludge, AVV internals might be fine just a blockage, might be a quick fix.

diplonics

Thanks for your advice, I already have the valve removed so I'll go the full hog and install a shut off valve and a new AAV.

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diplonics wrote: »

Thanks for your advice, I already have the valve removed so I'll go the full hog and install a shut off valve and a new AAV.

Sound, might be to late, if your near any industrial plumbing type distributors pick up an industrial type 1/2" AAV, never a problem with those, designed to last donkeys years, valve / vent construction slightly different that bottle type AAV.