An instantaneous water heater must have a properly sized valve to relieve pressure. What type of valve is required, not to exceed 150 pounds?

• A. Pressure relief
• B. Thermal expansion valve
• C. Check valve
• D. Shutoff valve

Answer: (A)

The main idea is having a safety device that automatically vents water when pressure gets too high. An instantaneous (tankless) water heater relies on a pressure-relief mechanism to prevent overpressure in the system. The appropriate device is a pressure relief valve, specifically a temperature and pressure (T&P) relief valve, which opens to vent water when the pressure reaches a preset limit—typically not exceeding 150 psi. This protects the heater and piping from bursting as the system heats or as flow is restricted.

The other valves don’t serve this safety purpose: a check valve prevents backflow, a shutoff valve stops flow, and a thermal expansion valve controls expansion in some closed systems but isn’t a safety release for overpressure. So the pressure relief valve is the correct choice.