Relief Valves

Temperature and pressure relief valves, boiler relief valves, safety relief valves and vacuum breakers, in 3/4" through 1-1/4".

A T&P valve is a safety device, not a plumbing fitting. It opens if tank temperature reaches 210°F or pressure reaches 150 psi, and a water heater without a functioning one can fail explosively. Never plug, cap or valve off the discharge.

The three ratings on the tag all have to be right: pressure setting, temperature setting and BTU relieving capacity. That last one is the most often ignored — the valve must be able to discharge at least as much energy as the appliance can produce, so a valve pulled from a 40,000 Btu heater is not adequate on a 199,000 Btu unit even though the threads match.

The probe length also matters. It has to reach into the top six inches of the tank where the hottest water sits; a short probe reads cooler water and opens late.

Boiler relief valves are pressure-only, typically 30 psi for residential hydronic. Materials run bronze, cast brass and lead-free alloys.

Brands include Watts, Cash Acme, Zurn Wilkins and Apollo-Conbraco.