Air Admittance Valve

[Driver]

We have an air admittance valve on the top of a waste stack outside a first floor a bathroom. The valve is about 50cms above the waste inlet from the toilet. This has been there for 20 years plus and has never been a problem. About a week ago when the toilet was flushed the water rose up the bowl but did drain out quickly. I thought we had a blockage and used a plunger to no avail. Since then I've had 2 plumbers look at it who both used a plunger again to no avail. However the second one took the air admittance valve off the stack and then when the toilet was flushed it emptied as normal.

I have now bought a new valve but the problem remains the same. With the valve off the toilet empties normally, with it on the water rises up the bowl.

Any suggestions anyone.

 

[snowhead]

You have a blockage lower down in the stack.

 

[rpm]

The new valve is faulty?

 

[CES]

As snowhead, you have most likely a blockage further down the line.

 

[Dotty]

That's 3 for the blockage.

 

[chris watkins]

That's 3 for the blockage.

Make it 4 for the blockage.

 

[rpm]

Are you guy`s saying it`s a full on blockage or a major restriction, If it`s a blockage then where`s all the water going? Not being funny here just wanna know.

 

[Koogatubac]

5 for a blockage, ive had this same problem about 20 times all on a brand new housing site

 

[Koogatubac]

When you're removing the AAV your creating positive pressure which in turns flushes since theirs a greater force.

because theirs a blockage theres greater negative pressure than positive thus your toilet is slow flushing/wont flush

 

[snowhead]

Near full on blockage, causing major restriction.
Enough to block initially when a flush occours, but given time the water will pass through the blockage.
The AAV restricts air being displaced from the stack and causes the discharge from the W.C to be part held in the pan. (Removing the AAV allows the discharge to release into the stack but not drain fully away immediately)

The solids will degrade and get flushed through over time, leaving paper to re-enforce the blockage.
In a Domestic little used property, this situation can survive for months and go unnoticed in an olde style fully vented, no AAV system.

In a system with AAV it's noticed far sooner.

 

[rpm]

Thanks snowhead for that explanation, now I`m here to learn not start a war but I thought an Air Admittance Valve let air out (but not in) or is it something to do with the rate that the air is let out?

 

[snowhead]

Clues in the title ADMIT....tance,, same as GOING INto Hospital

If it let air out there'd be smells let out as well.

Find an installed air admittance valve, close to a W.C
Tape a plastic bag with no holes in it (if you can find one) over the AAV.
Flush and Watch the bag collapse onto the valve and pipe.

 

[rpm]

Duh! Thanks again, really thought it was the other way round.

 

[Koogatubac]

Seriously ...

 

[rpm]

Seriously, To admit air out when under pressure.