The pressure relief valve, also as known as a blow-off valve, is a vital component of a boiler. Without a properly working valve, dangerous levels of temperature and/or pressure may build up in a home's heating system. Extreme pressure within the system could cause the boiler or water lines to rupture. If the temperature and pressure within the boiler are in the normal range and the pressure relief valve is leaking, it is a sign the valve is defective. Replace a defective, leaking valve right away.
Shut down the power to the boiler. In most cases, this will involve switching off the breaker specifically designated for the boiler. Also shut off the fill valve that supplies water to the boiler system. Wait a few hours to allow the boiler and water to cool.
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Drain water from the boiler in order to reduce the pressure. Open the drain valve on the boiler to drain the water. Watch the pressure gauge on the boiler. When the pressure is reduced to zero, close the valve to stop the drainage of water.
Attach a pipe wrench to the boiler's pressure relief valve. Loosen the valve and remove it from the boiler. If the valve has a drain pipe connected to it, remove the drain pipe prior to the removing the valve.
Wrap plumber's tape around all but the bottom two threads of the new pressure relief valve. Turn the new valve into the boiler and tighten it with the pipe wrench. When turning the new valve into the boiler, ensure it is straight and pointed in the same direction as the old valve. Reconnect the drain pipe if necessary.
Open the fill valve to refill the system with water and restore power to the boiler. Bleed the air out of the system by opening the bleed valves on your radiators. For most radiators, a screwdriver is required for operating the bleed valves. Check for leaks on the newly installed valve.