Why is water dripping from an overflow pipe?

A dripping overflow normally means a cistern is filling above its intended level because the float-operated inlet valve is not closing properly. Do not plug or cap the pipe: the discharge is warning you about the fault and giving excess water a safer route.

Work out which cistern it serves. A pipe through an outside wall may come from a loft cold-water cistern, a toilet cistern or another stored-water component. Look and listen without walking on unsupported loft surfaces or reaching into hot-water equipment.

If a toilet has an internal overflow, the water may run into the pan instead of outside. For a loft cistern, a raised water level, constant inlet noise or a float touching the lid supports the diagnosis, but the valve and cistern condition still need checking.

Arrange repair promptly. A valve that does not close wastes water and can leave the property relying on the overflow route. Any discharge associated with an unvented hot-water cylinder safety device is different: do not block or adjust it; use a competent installer.

Observe the pipe safely from ground level and note whether it drips continuously, only while water heats or after a toilet is flushed. Do not climb to an outlet or block it for a test. Inside, listen for a cistern filling when no water is being used. These details help a plumber match the outside symptom to the correct vessel. If water is entering the building, isolate the relevant supply if you can identify it safely and protect nearby electrics.

Marking which outside pipe is involved on a photograph can prevent confusion when several warning or waste pipes leave the same wall.

Sources

• Approved Document G — GOV.UK, accessed 14 November 2026.
• Approved Document G PDF — GOV.UK, accessed 14 November 2026.

On Leatmere

Read overflow pipes and the overflow pipe definition.