Water dripping from the outside pipe: pressure relief valve discharge

A discharging relief valve: the short technical version

The usual sequence is an expansion vessel that has lost its air charge, so heated water has nowhere to expand and pressure spikes every time the boiler fires. Overfilling via a filling loop left slightly open does the same. Once a valve has passed, debris on the seat often stops it re-sealing, which is why a vessel repair is frequently paired with a valve replacement.

Things worth knowing about a discharging relief valve

• Watch the gauge as the system heats — a big climb confirms the vessel
• Close and check both filling loop valves are fully shut
• A valve that has passed rarely re-seats perfectly afterwards
• External vessels can be fitted where the internal one is inaccessible
• Ignoring it wastes water and lets pressure fall between cycles

Questions we get asked

Can I just turn the pressure down?

Draining a little helps short term, but the vessel will still fail to absorb expansion on the next cycle.

Is the water dangerous?

It is system water, sometimes discoloured, and it can be hot. Keep it away from paths where it may freeze.

Where we deal with this

• Clutton (BS39) · 5 mi
• Ubley (BS40) · 8 mi
• Winford (BS40) · 10 mi
• Hilperton (BA14) · 10 mi