Possible Air Admittance Valve Fault

[Creeky]

Hi,
We have a weak flush issue in our main bathroom. I have changed the cistern, removed the toilet and checked for blockages in the soil pipe using a camera taped to a stick. I have found no obvious blockages in the vertical part of the soil pipe (as far as the camera can see). So from info found on the net I am assuming the soil stack is not letting air in correctly. I have looked on the roof (from ground level) and can not see the top of the soil stack, even though the neighbour has one.
So I can only assume we have an AAV fitted. I have been in the loft, but can not see the soil pipe rise above the ceiling. Where is it? Before I start breaking apart the box partition, Is it likely the AAV will be directly above where the stack rises?

I may seem like a silly question but I want to make sure I am along the right lines before I make a mess.

Thanks in advance.

 

[Tonycane]

Close coupled or low level wc?

 

[snowhead]

It sounds like the AAV will be boxed in , in the bathroom.

Where does the WC outlet go?

Wherever it is it needs an air supply otherwise it wont work, the box should have a vent in it.

It's more likely to be a blockage in the stack than a faulty / missing AAV

 

[Creeky]

Thank for the replies, The toilet is Low level WC, Concealed.

The WC soil pipe elbows immediately right then travels horizontally for couple of feet then joins a vertical pipe. The Sink and bath waste joins just below. The bath waste gurgles when a full sink is drained.

The soil pipe is boxed in in the adjacent room with no visible vent. There are no more toilet connected.

Thanks.

 

[Tonycane]

When you replaced the cistern did you check the inlet on the pan? I've had weak flushing toilets caused by the inlet holes being blocked by the syphon membrane breaking down and being flushed down and blocking the pan inlet holes. Pop the flush pipe out if you can and check. I would also change the aav.

 

[Creeky]

Hello Tony,
I did not check the pan Inlet, just the outlet (which was OK). I will check the inlet tomorrow and post results. I have read other posts on AAV issues, One resulting in a blocked drain external to the house, Is this worth a look before I knock holes in wall to find the AAV? As it does not appear to be in the loft space.
Also I have a toilet at the front of the house, which works ok. I guess the house has two soil stacks. Is this correct?

Thanks again for your help.

 

[Dsp]

Look in the loft space again for the soil stack it will be tight In a corner hidden by insulation and should have a polystyrene top on it
When you replace it read the instructions very carefully as often some of the packing is actually insulation and should be left on but a failing AAV usually lets out smells blockages cause flush problems

 

[Creeky]

Hi DSP,
I have checked the part of the loft directly above the vertical soil stack that is boxed in running up through the floors, removing insulation etc. There is nothing that resembles the top of a pipe or AAV. There is however a wasps nest one foot to the left of where I think the vertical part of the pipe is. But I may have my bearings wrong. So I will drill a small hole directly in line of the soil stack in the ceiling of the 1st floor into the loft space to see if I am looking directly in the right position. There appears no room to allow the pipe to shift left or right of the vertical pipe hidden from view as it enters the loft space, so I am assuming the AAV is hidden in the wall.

 

[Sparkgap]

Weak flush? Do I take it the water is slow to drain away from the WC?
The AAV should make no difference to flush as it's designed to ADMIT air to the sewer to prevent water traps being sucked out by a vacuum. If there's backpressure slowing down the WC I would expect to hear air bubbling back through the basin trap when you flush.
Just a thought, are the WC and cistern the same? Did have a case some years ago where old (2 gallon) WC had its cistern replaced with modern low flush one and you often couldn't get everything away with one flush.

 

[Creeky]

Hello spark.
The problem is when flushing the toilet water rises in the pan and is does not drain at normal speed. It does not fill to the top (as you would expect from a blocked toilet) but is just slow to drain the pan to the normal water level. I do get bubbling back if I drain a bath sometimes through the toilet and though the bath trap if I drain a full sink. But no bubbling during flushes it just running taps.
By asking if they are the same, I guess you mean are they connected, yes they are connected to the same vertical soil pipe.

The cistern was replaced due to this fault, which has not been cured so I guess it's not that and it's a 60 litre cistern.