Pressure reducing valve fault or failure
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Post a job — we'll find you an engineer →⚠️ A failed PRV that is stuck open will allow full mains pressure into the system — which can be 6–8 bar in some areas. This can stress appliances, pipework, and fittings designed for lower pressures. If you suspect a failed PRV, have it assessed promptly.
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Most likely cause & what to check
A pressure reducing valve (PRV) is a brass valve fitted to the incoming water main — usually just inside the property or in the airing cupboard. Its job is to reduce the incoming mains pressure (often 4–8 bar) to a safe working pressure of 2.5–3.5 bar for internal pipework.
Signs of PRV failure: if it sticks closed, you will experience low flow throughout the house; if it sticks open, you will have excessively high pressure causing tap washers to fail quickly, appliances to leak, and in extreme cases water hammer.
You can check the pressure with a gauge — screw-fit pressure gauges (£10–£20) attach to a tap or hose bib and give an instant reading. Normal domestic pressure should be 1.5–3.5 bar. Above 4 bar is high, above 6 bar is dangerously high.
PRVs can sometimes be adjusted — there is a central screw or cap nut that can be turned (clockwise to increase, anti-clockwise to decrease the set pressure) using a spanner. However, if the valve is old, worn, or corroded, adjustment may not be effective.
Replacing a PRV requires isolating the mains supply (turning off the main stopcock), cutting out the old valve, and fitting the new one. Always fit with the arrow on the body pointing in the direction of flow. A typical PRV costs £30–£80; a plumber will charge 1–2 hours labour.
After fitting, have a pressure gauge connected downstream to verify the outlet pressure is set correctly before commissioning.
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