What happens if a PRV fails open or closed?

A Pressure Reducing Valve (PRV) is designed to maintain a consistent, safe water pressure downstream from the main supply. When a PRV malfunctions, it typically fails in one of two ways, each with distinct consequences for the plumbing system.

Failure Open: Consequences of Overpressure

If a PRV fails in the open position, it no longer restricts the incoming high-pressure water. This leads to unregulated, high water pressure throughout the downstream system. Symptoms include banging pipes (water hammer), excessive noise from fixtures, leaking water heaters, burst pipes, and damage to appliances like washing machines and dishwashers. Overpressure can also void appliance warranties and increase water consumption.

Failure Closed: Consequences of Underpressure or No Flow

Conversely, if a PRV fails in the closed position, it severely restricts or completely blocks water flow. This results in very low water pressure or no water at all at faucets, showers, and other outlets. It can impact daily activities like showering and appliance operation, and in some commercial or industrial settings, it could lead to critical process failures or safety concerns where consistent water supply is essential.