Boiler Pressure Relief Valve Dripping in Greater Vancouver

A dripping pressure relief valve is a signal that something in the boiler system is causing excessive pressure — and it must be investigated, never plugged or bypassed.

What This Symptom Means

The pressure relief valve (PRV) is designed to open and release water when system pressure exceeds its setpoint (typically 30 psi for residential boilers). A dripping PRV means the system is approaching or reaching that limit, or the valve itself has deteriorated and is weeping at lower pressure.

Common Causes

• Expansion tank waterlogged or failed — cannot absorb pressure rise during heating cycle
• System pressure set too high at the fill valve — cold fill pressure too close to relief setpoint
• PRV itself has deteriorated — the valve seat is no longer sealing reliably
• Backflow preventer failed closed — preventing system pressure from equalizing with supply
• Thermostat or aquastat set too high — system overheating and raising pressure excessively
• Blocked circulation creating localized pressure spikes

What Homeowners Can Check Safely

• Do not cap, plug, or tie the PRV discharge pipe — this is a life-safety component
• Note whether the valve drips during heating (pressure-related) or constantly at rest (valve failure)

When to Call a Licensed Technician

Boiler systems involve pressurized hot water, gas, and electrical components. Do not attempt to open sealed components, adjust gas pressure, or bypass safety controls without professional diagnosis.

• Expansion tank inspection, draining, and replacement or recharging
• System pressure analysis during a full heating cycle
• PRV replacement — PRVs that have opened should typically be replaced regardless of cause
• Aquastat temperature setting verification
• Fill valve and backflow preventer inspection

Frequently Asked Questions

Can I replace the pressure relief valve myself?

PRV replacement involves working with a pressurized boiler system and gas appliances. While some experienced homeowners do this task, it is recommended for a licensed plumber or HVAC technician. The valve must be matched to the boiler pressure rating, and the system must be depressurized and drained at the boiler before removal.

Why does my PRV only drip when the boiler is running?

This is a classic sign of a waterlogged expansion tank. When the boiler heats water, it expands. The expansion tank is supposed to absorb this expansion. If the tank bladder has failed and the tank is full of water, it cannot absorb the expansion — system pressure rises until the PRV opens. Replacing the expansion tank usually resolves this immediately.

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