Pressure Relief Valve Function & Failure
Every boiler has a relief valve to vent excess pressure and prevent tank rupture. When it leaks continuously, the internal seal or spring mechanism has worn out over 10-15 years. A slow drip (2-5 drops per minute) during heating is normal as pressure rises; continuous drips at rest indicate valve failure and need replacement. Cost: $200-$400 total (parts + labor).
Mineral Buildup & Hard Water
Hard water minerals (calcium, magnesium) accumulate on the valve seat, preventing it from sealing tightly. This is especially common in Greater Vancouver where water hardness is high. Mineral buildup is the #1 cause of relief valve sticking or leaking. Solution: install a whole-home water softener ($800-$1,500) or use boiler-specific descaling additives ($50-$100 per treatment). Regular flushing (every 3-5 years at $200-$400) removes sediment and extends valve life.
Overpressure & Tank Stress Risk
A failing relief valve that no longer opens properly allows system pressure to climb above 30 PSI (the safety threshold). Sustained overpressure stresses boiler tank seams and welds, accelerating corrosion and creating risk of tank rupture. Do not ignore a leaking relief valve — early replacement ($200-$400) prevents expensive tank replacement ($2,500-$6,000) and potential flooding damage.
Replacement Process & Timeline
Pressure relief valve replacement is straightforward: technician shuts off the boiler, drains part of the system (2-3 gallons), removes the old valve using a wrench, installs the new valve, refills the system, bleeds air from radiators, and pressure-tests. Total time: 1-1.5 hours. Cost: $200-$400 (relief valves are $60-$150, labor is $100-$250).
Prevention Through Maintenance
Have your relief valve pressure-tested annually as part of regular boiler maintenance. Install a whole-home water softener if you have hard water — this prevents mineral buildup on internal components. Use a boiler system additive during annual service to inhibit corrosion and scale. Keep system pressure between 12-15 PSI at rest to minimize stress on the valve. Early maintenance ($50-$150/year) prevents expensive repairs.