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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Frequently asked questions
What is a pressure reducing valve and do I have one?
A pressure reducing valve (PRV) limits the incoming mains pressure to a safe level for your household plumbing — typically 1.5–3.5 bar. Most modern properties built after the 1990s have one, usually on the rising main near the meter or under the kitchen sink. If your mains pressure is very high, you almost certainly have one.
How do I know if my PRV has failed?
Signs of a failed PRV: banging or water hammer when taps are closed, unusually high pressure at the taps, repeatedly tripping pressure relief valves on the boiler or unvented cylinder, or conversely — very low pressure if the valve has seized shut. Both extremes indicate a PRV issue.
Can a PRV be adjusted without replacing it?
Yes — most PRVs have an adjustment screw that allows the output pressure to be set within a range (typically 1–4 bar). However, adjustment requires a pressure gauge to set correctly, and should only be done by a qualified plumber if the valve is otherwise in good working order.