Gurgling toilet when the shower runs — what it means
If the toilet gurgles when you run the shower, basin or washing machine, your soil vent isn't doing its job. Here's why and what to do.
When water drains from one fitting it has to be replaced with air, or the system goes into negative pressure. That's what the soil vent is for — it lets air in at the top of the stack as water flows out at the bottom.
If the vent isn't doing its job, the next nearest U-bend (usually the toilet trap) gets sucked dry, and you hear the characteristic 'glug' as air pulls past the water seal.
What causes it
- Vent blocked at roof level — bird's nest, leaves, frost cap not removed
- Vent capped during building work — common after loft conversions, with no air admittance valve fitted in its place
- Vent disconnected under the floor — older properties where lead joints have failed
- Partial blockage downstream — the system can't shed water fast enough, creates back-pressure
How to narrow it down
- Gurgle on every fitting drain = vent issue. Almost certainly.
- Gurgle plus slow drainage on multiple fittings = downstream blockage. Plunger the toilet first, then call us if it doesn't stop.
- Gurgle only on the shower or basin = trap issue local to that fitting.
Why you shouldn't ignore it
If the U-bend keeps getting sucked dry, sewer gas comes back into the house — especially noticeable at night when nothing's been used for hours. Long-term, hydrogen sulphide is corrosive to metalwork and unpleasant to breathe.
How we fix it
- Inspect the vent at roof level (we carry ladders and access kit)
- Clear any blockage, or install an air admittance valve (AAV) inside the property if the original vent can't be restored
- CCTV the soil run if there's any suspicion of a downstream partial blockage
Typical job: half a day, £150–£350 + VAT depending on access and what we find.