Condensate pipe leaking inside

The condensate pipe carries slightly acidic water (pH 3–5) from the boiler to a drain. It is plastic waste pipe, typically 21.5mm. Leaks are usually from push-fit joint failures.

The condensate water is not hazardous but is mildly acidic. Wipe up spills promptly and rinse with water.

Locate the leaking joint — dry the pipe and observe where water appears. Push-fit joints can pull apart if the pipe moves or was not fully inserted.

To fix a push-fit joint: cut the pipe squarely 50mm above and below the failing joint using a hacksaw or pipe cutter. Fit a new push-fit connector (21.5mm waste push-fit coupler — £2–£5 from any plumbers' merchant). Push both pipe ends firmly into the coupler until they click.

If the pipe is cracked (this can happen when it freezes in winter), cut out the cracked section and splice in a short piece of new pipe using two couplers.

Ensure the condensate pipe has a continuous fall toward the drain — at least 2.5° (approximately 44mm drop per metre). A sag in the pipe where it can pool and freeze is a common installation fault.