blown aav

[Shnorbits]

I have an old worchester bosch 230 combi gas boiler 11year old. Awoke thismorning to find lots of water dripping from under boiler. There was water over the electrics, most of boiler. After mopping up, it appears the water coming from aav. Black valve found in bits, at base of boiler housing. No water & no pressure in boiler. Tried to add water via loop, poured out of the small hole on side of aav.
Q1 What is possible cause of valve having blown?
Q2 Is it safe to go ahead & replace the aav?
Q3 New valve is different height from old one? The 3/8 thread hole is longer than excisting one. The valve is ontop of new one, not at side as excisting one. Book says part number is correct. But do u think i Have got wrong one?
Its starting to get a little cold around here............

 

[Gasguru]

Sometimes debris becomes trapped in the valve seating leading to the water loss.

Don't worry about the new part, you may find it requires sealing with PTFE tape wound to a taper.

However the leak may have caused more damage than you think. Did the water level reach the gas injector? If so the gas valve may have become damaged. Sometimes the burner and pilot assembly can become waterlogged. The boards will require thoroughly drying out. Even then it is possible the relays may not be sealed and have become contaminated.

I would advise you get someone in since the work involves the gas train.

Check the expansion vessel whilst you're at it.

 

[Shnorbits]

Boards are dried and and new valve fitted in fine, boiler now comes on fine for hot water and central heating. However the pressure in the boiler rises above the normal level worrying me to the point i shut the boiler off, could this be due to air in the system?

Thank you for your reply
shnorbits

 

[Gasguru]

Check the expansion vessel whilst you're at it.

See the FAQ's

 

[Shnorbits]

Checked & Expansion vessel air valve sprays water, does this mean diaphragm gone & i need a new expansion vessel. Could this also have caused the aav to fail orriginally

regards Shnorbits

 

[Gasguru]

I hope you are checking the expansion vessel pressure with the system pressure gauge at zero.

A very small initial quantity of water is not unusual since the valve is low down.

Any more than that and the vessel diaphragm is holed.

Normally cheaper to plumb in an additional vessel elsewhere (eg coming off the filling loop connection).

The leaking aav is probably unrelated.

 

[Shnorbits]

expansion vessel seems to have a fair amount of water in it
turned on boiler and pressure gauge reading doubled (started at 1 bar and doubled to 2 bar) within 5 minutes, its not normally that high


regards shnorbits

 

[Gasguru]

Have you tried pumping up the vessel as described in the FAQ's?

Of course the pressure will rocket if the vessel has insufficient air..that's the purpose of the vessel...to absorb the extra volume of water as it heats up.

 

[Shnorbits]

Right i emptied my system as the FAQ's describes, with the system pressure at zero and one of the radiator bleed valves open the expansion vessel would not pressurize. So i tried pressurizing with the rad screw in and got it up to 9 PSI however the system pressure also increased to half a bar. I'm not sure if im doing this right but i thought pressurizing the vessel could be done with the system open however i cant get my vessel to pressurize unless i've got a closed system.

Regards Shnorbits

 

[Gasguru]

Initially when pumping up the vessel you will expel the water within the vessel. This is why you must have the system side open. However if there is a hole in the diaphragm the presurised air will pass striaght through the diaphragm and hence no pressure increase on the air side.

Replace the vessel or leave the boiler vessel in place and plumb in an additional vessel (say 8 litre).

 

[Shnorbits]

Finally we have heat..... thanks so much. Located, purchased & fitted one expansion vessel. A bit fiddly, but with patience and an extra pair of hands from the nipper and of course following installation instructions, I now have a working boiler. Pressure has stayed put now for almost 2 hours, so keeping fingers crossed....

cheers again