Auto air valve failed, again!

[MuddyMike]

Our five year old Mexico HE36 gas boiler needs yet another auto air vent valve. It was replaced in the final months of warranty due to it leaking and dribbling water onto the electrics causing the trip to go. Parts Centre are the only stockist I can find that have one, and one only! Is in the Portsmouth branch but they are sending it up to me "next day" delivery for four quid postage. That's not bad as it would have cost more then that in diesel for me to have driven to the nearest branch

Anyone else aware of this being a regular failure on these boilers?

Mike

[YAPH]

Mucky system water? AAVs have fairly dainty mechanisms which work better in clean water than gritty mud :-)

[cynic]

Honeywell do a version with a screw down cap which has a fibre washer. With the cap open the valve will vent air from the system. Once clear screw the cap down and if any air/hydrogen does accumulate it opens the valve and collects under the cap. This causes the fibre washer to dry out and shrink, allowing the air to escape. If fluid reches the fibre washer it expands again and closes off the vent. Another option is to extend the air discharge point via a tube to somewhere safe. Then any minor weep will not cause damage to your electrics. Unless you have a problem elsewhere the air vent should not be needed after a couple of weeks as all the air should have left the system.

[Onetap]

On Jun 3, 10:05=A0pm, cynic wrote: .

Yes, it's a regular point of failure on any AAV. They should only be used to get the air out after filling and then the cap screwed down. If more air accumulates, there is a problem somewhere; automatic air venting should not be needed.

There was one design (expensive ISTR) that had the air release valve above the float and connected by a linkage, the idea being the mucky water didn't get near the valve.

[Andrew Gabriel]

It's a regular failure of these valves. You can't leave them open all the time, as the seal relies on being wet, which leaves an area which will dry and form scale, and then no longer seal.

You may be able to recover it by flushing descaler through, although it won't be pure scale, but mixed with other things in the heating system water, so it might not work.

[YAPH]

No, that's the fibre-washer type. Bottle type AAVs have a float which, when it rises, closes a hole above it which (when there's air in the system and the float isn't floating) lets the air out. It's the suspension of the float mechanism that I referred to as dainty. These types of AAV do usually have a sealing cap but these can usually be left partially unscrewed to act as a dust cap whilst allowing air out.

[MuddyMike]

This is the valve.

have plugged the leak with the set screw and nut you see in the top, Bit fuzzy that picture, must check before uploading in future.

Mike

[Andrew Gabriel]

It's the bottle type I'm refering to. The float seal will be wet when sealing, which means there's going to be some moisture on the outside of the seal, which evaporates and leaves scale. Eventually, the sealing surface becomes contaminated with scale, and stops sealing.

I usually leave mine open for a week after refilling, and then close it.

[YAPH]

least of your worries ;-/

[YAPH]

The float seal may get wet and eventually suffer scale build-up if air escapes vigorously causing water to spray out but I'd expect the rising float to cut off the air escape port before the water level reaches it. In theory of course: in practice whatever is in the water *will* get everywhere and bugger it up eventually. :-(

[MuddyMike]

No its £2000 worth of Mexico HE36, not without trouble mind :-(

Mike