Air gurgling out the sink waste when flushing toilet

[letmedoit]

My Mum's house had a bedroom and shower-room loft conversion 18 years ago. The room is used very little (last time 8 months ago), but I stayed there last week on a visit.

When I flushed the toilet the water built up in the pan till almost full, then rushed away. As it went, air gurgled out of the sink and shower waste. Likewise, air gurgles out of the toilet when the sink drains. During this a sort of groaning noise comes from the space within the eaves.

As there is no vent pipe visible I guess there must be an air admittance valve in the roof void. Could this be sticking due to lack of use (in which case I will try to access it on my visit again next month) or is it a sign of a blockage somewhere in the soil pipe/drain ?

Thanks

 

[Hugh Jaleak]

Sounds to me like there's a blockage. Air admittance valves do just that, let air in. If the drain is blocked, and you then flush the WC, you are put another 6-9 litres of water into what is effectively a sealed pipe. The water needs to displace some air, so the positive pressure is released back through the point of least resistance, meaning the noise you here may well be air coming back through the traps.

Trace where the stack goes to outside the building, and check any inspection chambers are free flowing.