Toilet not flushing: causes and what to do

Four different causes

• clog at the bowl outlet or in the drop pipe — water rises and falls slowly
• cistern doesn't fill or the valve doesn't open fully — water comes weakly
• ventilation pipe is blocked — flush lacks draw and there's a gurgling sound
• shared sewer is clogged — the problem also shows up in other fixtures

How to check the cause yourself

First look inside the cistern. If the water doesn't reach the marked level or the valve closes too early, it's a technical issue, not a clog.

Pour about five litres of water into the bowl at once. If it goes down freely, the pipe is passable and the problem is with the flush. If the water rises, the clog is real.

What to avoid

Don't push wire or a sharp object into the bowl — the bowl's internal collar cracks easily and then a new bowl is needed. Also avoid repeating several different chemicals one after another, since the water isn't moving and the product just sits there.

When the problem is in the cistern

Inside the cistern there are two components: the fill valve and the outlet valve. If filling is slow, the water comes weakly and the flush is left incomplete. If the outlet valve's seal is worn, water quietly keeps running into the bowl and there's no pressure left for flushing.

Both components can usually be replaced without moving the bowl. With a concealed cistern the work is done through the maintenance hatch and requires more precise part selection, since access is limited.

When the problem is in the pipework

If the five-litre test shows the water rising, there's a clog at the bowl outlet or beyond it. The section inside the flat can be opened with a drain snake; for the shared drop pipe and stack, pressure flushing is needed along with access to an inspection hatch.

In an apartment building it's worth agreeing beforehand on when water won't be used. Water coming from above can spill out through an open inspection hatch, and the work would then have to be paused.

When it's sensible to replace the bowl

If the bowl's internal flush channel is clogged with limescale or the ceramic is cracked, repair won't give a lasting result. The same applies when the old bowl's outlet no longer matches the existing connection and every seal replacement ends in leaking.

What's worth mentioning when booking

Describe whether the water rises in the bowl or the flush comes weakly, whether the problem is only in the toilet or also in the sink and shower, and whether neighbours have the same issue. These three answers help assess, even before arrival, whether the problem is more likely in the cistern or the pipework, and prepare for the job better.

It's also useful to mention the bowl type: a wall-hung bowl with a concealed frame, a floor-standing bowl with a separate cistern, or a compact combo unit. With a concealed frame the work goes through the maintenance hatch and the choice of parts is narrower.