Pressure Relief Valves: The Safety Device You Shouldn't Cap
The pressure relief valve is a safety device that opens automatically if system pressure climbs too high, discharging water outside rather than letting pressure build to a dangerous level.
The pressure relief valve is a safety device that opens automatically if system pressure climbs too high, discharging water outside rather than letting pressure build to a dangerous level. A dripping one is a symptom to investigate, never something to plug or ignore.
What it does
A spring-loaded valve set to open at a fixed pressure, usually 3 bar on domestic systems, protecting the boiler and pipework from over-pressurisation.
How it fails
Debris or scale sits on the seat and it weeps continuously, or the spring weakens with age so it opens earlier than it should.
Repair or replace
A valve that's weeping due to debris can occasionally be freed by operating it, but a valve that won't reseat cleanly is replaced rather than repaired.
Questions we get asked
Can I just cap the discharge pipe?
No. Capping a safety discharge pipe removes the protection it exists to provide and isn't something we'd ever recommend or do.
Is this Gas Safe work?
On a gas boiler the relief valve is part of the appliance, so it's Gas Safe registered work; on some system layouts it may sit apart from the boiler as a plumbing item.
Why is it dripping only sometimes?
Intermittent weeping often follows the heating cycle, which usually points to pressure creeping up as the system heats rather than a constant leak.