AAV on a soil stack.

[traineedrip]

called out to a blocked toilet, nothing physically blocking the pipe but water backing up in pan. Has an indoor short soil stack next to W/C. removing the cap and activating the aav manually and the toilet empties perfectly. letting the valve rest on top of the stack without cap and it bounces up and down letting air in but valve wont open.... so theres some pull through the pipe when flushing.

Valve seems clean and not stiff, cant really understand what could fail on it.

Got onto hunter plastics, who suggested replacing it but couldnt offer any explanation as to its failiure. its an s450 aav 110mm.

So, how often do these things fail? why? and is it possible its something else is causing the poor drainage?
system has worked fine up until now, top of stack is about basin height and theres 2 basin wastes also sharing it... which appear to be fine.

 

[Toddyplumb]

Nothing wrong with AAV drain is blocked

 

[traineedrip]

why are you saying that mate? How can there be a blockage if the water runs freely without it?

 

[Toddyplumb]

You said the water was backing up in the pan ?
Sounds like you are getting back pressure it makes the AAV bounce
Have you checked the manhole ?
It doesnt have to be fully blocked !
The AAV should be above the basin spill level

 

[traineedrip]

yep water filling up the pan before gently flowing away. soil pipe clear, and stack also clear. It did have several flushes with me peering down the stack and water flowed perfectly, without backing up in the stack. Can see what your saying though. How much of a partial blockage would the aav need to render it non effective? I didnt lift the manhole as I couldnt see any blockage evidence

 

[Toddyplumb]

Try the manhole as the water hits a partial blockage it sends an air shock wave back up the drain, its worth a look.
We get our AAV rattling when the manhole 300metres away starts to back up !

 

[traineedrip]

Just read this...
Problems can arise where air admittance valves are fitted to vent pipes which are not separately vented and which include water traps - this can lead to back pressure in the pipework when an appliance is discharged which will effect the appliance discharge - this will be especially noticeable when a toilet is flushed.

There is a sink waste and basin waste so could it be anything to do with them? Ill check the manhole as you say and try plugging the wastes and overflows and see if changes anything.

 

[traineedrip]

Right then. Update.
I gave the job up and suggested dynorod. Reason being that any draincovers will be in a busy shopping area and ive no barriers. Ive just been given the job back as they say it needs a new valve! Worryingly though, they also reckon they cant find the drain! Some experts!

Im going to replace the valve and see if it cures it but if they havnt lifted any manholes ive little faith.