RMC HT55 700 Kpa 15mm Pressure Temperature Relief Valve HT503 are safety controls which ensure that the temperature of the water in a pressurized unvented water heater cannot exceed 99˚C in the event that the normal thermostatic controls fail. These valves may be used to guard against over temperature and over-pressure hazards wherever water is stored in unvented containers. This is a requirement of Australian Standard AS 3500-4. The pressure and temperature relief valve should be installed at the heater. System inlet pressure should be no higher than 80% of the set pressure of the P&T Relief Valve. Ensure that the set pressure of the High Pressure Expansion Control Valve is suitable for use with the water heater it will be installed with. It is recommended that the easing lever be actuated every six months to prevent accumulation of mineral deposits that may impair valve operation. Lever should be operated smoothly as a sudden influx of water may cause the auxiliary pressure relief device to activate. Relief Valve Selection Guide Determine the pressure & temperature pressure setting Check You Have the Correct Pressure &Temperature Valve Configuration 1. If the water heater is a new installation, check that the P&T valve provided is rated the same as the working pressure of the water heater. 2. If the valve is a replacement valve (e.g. for maintenance purposes), ensure that the replacement P&T valve is of the exact same configuration and pressure setting as the valve it is replacing. Installations with an Expansion Control Valve Determine the correct valve combination match the Reliance P&T relief valve with an expansion control valve with a rating cap of the same colour.