Domakihub How to Replace a Stopcock: A Step-by-Step Plumbing Guide
Know what the job involves, prepare properly, and get it done right — or know when to call a plumber.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
A failing stopcock — the main shut-off valve on your rising water main — can turn a minor leak into a flooding emergency in seconds. The video above walks through the physical swap; this guide adds the context you need to prepare the job, choose the right fitting, and decide whether a confident DIYer can handle it or whether a licensed plumber is the safer call. For properties in Greece — apartments, holiday villas, and hotels alike — the mains stopcock is usually located under the kitchen sink or in a utility cupboard, and local water supply pressure can vary significantly by region.
What a Stopcock Is and Why It Fails
A stopcock (also called a stop tap or shut-off valve) is a quarter-turn or gatevalve-style fitting that controls the entire flow of mains water into a property. When you turn it clockwise it closes; counter-clockwise it opens. Most Greek properties use either a compression-fit brass stopcock or a lever-type ball valve on 15 mm or 22 mm copper pipe.
Stopcocks fail in two main ways. The gland packing inside the spindle dries out and water weeps past the spindle when the valve is in use — you will see a slow drip around the handle. Alternatively, the valve body corrodes or the internal rubber washer deteriorates so the valve can no longer fully stop water flow. Neither fault will repair itself, and a valve that cannot close fully is dangerous in any emergency.
Is This a Job for a DIYer or a Licensed Plumber?
Replacing a stopcock sits in a grey zone: it involves only the cold-water mains, not gas or live electricity, so there is no statutory requirement in Greece for a licensed plumber to do the work. A confident, careful DIYer who understands how to isolate the supply and work with compression fittings can do it. However, there are situations where calling a licensed plumber (idravlikos) is strongly recommended: if the property is still under building warranty, if your water meter cupboard is sealed by the municipal water authority (EYDAP or local DEYA), if the pipes are in poor condition or are plastic push-fit you are unfamiliar with, or if you cannot fully isolate the supply before the existing stopcock.
Note that the isolation point upstream of your stopcock — typically the mains ferrule cock or meter valve on the street — is the property of the water utility. Opening or closing that valve yourself may be prohibited by your supplier. Always check with your local DEYA before touching it.
How to Replace a Stopcock: The Full Process
- 1
Isolate the water supply upstream
Before touching anything, identify the isolation point upstream of the existing stopcock — this is usually the water meter valve in the meter box at the boundary of the property, or a second isolation valve on the mains pipe. Turn it fully clockwise to close. Open the cold kitchen tap and let it run until water stops flowing, confirming the supply is off. Have towels and a bucket ready under the pipework.
- 2
Drain and prepare the pipe section
With the supply isolated, open the existing stopcock fully to drain any residual water from the pipe between the isolation point and the valve. Use a pipe slice or hacksaw to cut the pipe cleanly at least 30 mm on each side of the old stopcock body, leaving enough straight pipe to work with. De-burr the cut ends with emery cloth so they are smooth and round — rough or oval pipe ends are the most common cause of compression-fitting leaks.
- 3
Remove the old stopcock
Undo the compression nuts on both sides of the old valve using two spanners — one to hold the valve body and one to turn the nut — so you do not twist the pipework. If the nuts are seized, apply a short burst of penetrating oil and wait ten minutes before trying again. Once removed, clean the pipe ends thoroughly and check that the olive (the small brass ring that creates the seal) on each side is not damaged. Replace olives if they are deformed; they are inexpensive and a fresh set eliminates uncertainty.
- 4
Fit the new stopcock
Slide the compression nuts onto the pipe ends (thread first), then slide on new olives. Offer up the new stopcock — check the flow arrow cast into the body matches the direction water travels toward your property — and hand-tighten the compression nuts onto both ports. Using two spanners, tighten each nut by one and a quarter turns past hand-tight. Do not over-tighten: brass compression fittings seal on the olive, not on thread force, and over-tightening deforms the olive and creates leaks. Wrap PTFE tape on any threaded connections (not on compression) if your replacement valve uses a threaded inlet.
- 5
Restore pressure and check for leaks
Slowly open the upstream isolation valve a quarter turn to allow water to fill the pipe gently. Watch both compression joints for drips. If a joint weeps slightly, give the nut a further quarter-turn — no more — and wait thirty seconds. Once both joints are dry, open the stopcock itself fully and restore flow to the property. Check the joints again after five minutes under full pressure. Run each cold tap in sequence to purge air from the system before using any appliances.
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FAQ
- Can I replace a stopcock without turning off the street supply?
- Only if there is a functioning isolation valve upstream of the existing stopcock that can fully stop the flow — for example, a lever-type ball valve installed before the stopcock. If the only upstream isolation is the water meter valve or the ferrule cock on the street main, you or your plumber will need to close that. In many Greek municipalities the meter valve is sealed or owned by the utility (EYDAP/DEYA), so contact them first.
- What size stopcock do I need for a typical Greek apartment?
- Most residential rising mains in Greece use 1/2-inch (15 mm) pipework, which matches a standard 15 mm compression stopcock. Older buildings — particularly those built before the 1980s — may have 20 mm or even 22 mm copper or iron pipe. Measure the outside diameter of the pipe before buying: 15 mm OD = 1/2-inch fitting; 22 mm OD = 3/4-inch fitting. When in doubt, take a short cut piece of your pipe to a plumbing merchant.
- How do I stop the stopcock spindle from dripping without replacing the whole valve?
- If only the spindle is leeping and the valve body is otherwise sound, you can often fix it by tightening the gland nut (the small nut around the spindle shaft) by a quarter-turn. If that does not stop the drip, the gland packing needs replacing: close the valve, undo the gland nut, pull out the old packing (hemp or graphite cord), wind in new PTFE or hemp packing, and re-tighten. This is a cheaper repair than full replacement and worth trying first on a valve that is otherwise closing correctly.