Replacing a Stopcock: Job, Time and Cost

When a stopcock needs replacing, not repairing

A gland drip or a weeping nut can usually be cured in place, as our guide to fixing a leaky stopcock explains. Replace the valve instead when any of these apply.

• It leaks from the brass body, or the body has a white powdery crust or a pinkish tinge from dezincification
• It closes fully but water keeps passing through to the taps
• The handle spins without tightening, or the spindle has snapped
• It is seized and has already been freed once or twice
• It is buried under a floor, behind a fitted unit or in a spot nobody could reach in a hurry

Your inside stopcock is your responsibility. Thames Water says so directly: because it is in your home, it is yours to install, maintain, fix and replace. The outside stop valve in the pavement is the water company’s.

How the job is done, step by step

This is what a competent plumber does, and what you would be taking on yourself. The order matters, because the stopcock is the first valve inside the house and cannot be used to isolate itself.

• Shut the water at the outside stop valve, usually under a cover in the pavement or in the meter chamber, turning clockwise with a stopcock key. If the supply is shared, the neighbours lose water too and need warning.
• If the outside valve is seized, missing or feeds a whole block, freeze the pipe instead. A pipe-freezing kit clamps round the pipe just before the stopcock and forms an ice plug that holds back mains pressure while the valve is changed.
• Open the lowest cold tap in the house to drain the pipe, with a bowl and towels under the old valve.
• Undo the compression nuts, or cut the pipe either side if the old valve was soldered. Cut the old olives off, and trim back any pipe that is scored or out of round.
• Fit the new valve with new olives, with the arrow on the body pointing the way the water flows, towards the house. Hold the body with one spanner while tightening each nut with another.
• Restore the supply slowly, check both joints and the spindle dry under full pressure, then run the taps to clear air.

Which replacement valve to choose

The arrow matters more than it looks. A traditional stopcock has a loose jumper inside that lifts off its seat when water pushes from below. Fit it backwards and the water pressure holds the jumper shut, so you get little or no flow however far you open it.

All fittings on a drinking water supply have to comply with the Water Supply (Water Fittings) Regulations 1999, so buy from a plumbers’ merchant or a recognised brand rather than an unmarked online valve. The common choices are these.

• Traditional brass stopcock with a crutch handle, 15mm or 22mm compression: the cheapest option, a few pounds at a DIY store. Choose DZR (dezincification-resistant) brass so the body does not go porous in future.
• Quarter-turn lever valve: shuts with a single 90-degree turn, which anyone can do in the dark. The better choice for most homes, especially where an older relative or tenant needs to use it.
• MDPE stopcock with compression ends for a blue plastic supply pipe: common in newer homes and where the supply comes up through a solid floor. The pipe needs a liner insert in each end so the joint grips.
• Remote stopcock such as Surestop: the valve on the pipe is operated by a switch mounted somewhere convenient. It costs several times more than a plain valve, but it solves the problem of a stopcock in the back of a cupboard or under a floor.

How long it takes and what it costs

A like-for-like swap of an accessible stopcock, with a working outside stop valve, is about an hour on site including testing. Add time for anything that makes it harder: a seized outside valve that means freezing the pipe, a lead or old iron supply pipe that needs an adaptor, a valve buried in a floor void, or moving the stopcock to a better position.

Parts are the small part of the bill. A plain 15mm brass stopcock costs under £10; a quarter-turn DZR valve a little more. Most of the cost is the visit and the labour, and it rises with the complications above rather than with the valve itself.

Two sensible additions are worth doing at the same time. A drain-off valve fitted just after the new stopcock lets the house be drained in future without disconnecting anything; the Regulations require systems to be capable of being drained down and fitted with enough drain taps and servicing valves. And if the old stopcock was hard to reach, moving it to an accessible spot now saves a panic later.

For an emergency visit, the £60 call-out applies at any hour, and the repair price is agreed with you on site before any work starts. Our pricing page explains how that works.

Can you replace a stopcock yourself?

If you are comfortable making compression joints, the outside stop valve works and the stopcock is on copper pipe in an accessible spot, it is a manageable DIY job. The risks are specific: an outside valve that will not quite shut, so water keeps coming while the pipe is open; a scored pipe that will not seal with a new olive; or a nut overtightened until it splits.

Leave it to a plumber if the outside valve is shared, seized or cannot be found, if the supply pipe is lead or galvanised iron, if the stopcock is in a flat and the riser feeds other homes, or if you have no way to get the water back off quickly should a joint fail. A burst on the incoming main has nothing upstream of it inside the house to stop it.

Lead supply pipes and moving the stopcock

In older London houses the stopcock is often where a lead supply pipe from the street meets the copper inside. If yours is on or next to lead, a replacement is a good moment to ask about the supply pipe as a whole. Lead supply pipes are mostly found in houses built before about 1970 (see how to tell if you have lead pipes), and the joint between lead and copper needs a proper lead-to-copper connector, not a standard compression fitting.

The supply pipe from your boundary to the house is your responsibility too, so replacing it is a bigger job with its own considerations. Our guide to who owns the water pipe to your house sets out where your side ends. For the replacement itself, see stopcock repair and replacement.