PLUMBCRATE
How to fit an isolating valve (15mm, step by step)
Quick answer: to fit an isolating valve, turn off the water at the stopcock and drain the pipe, cut out a short section of pipe to suit the valve length, deburr the ends, slide a compression nut and new olive onto each pipe end, push the valve on so any flow arrow points the way the water travels, and tighten each nut hand-tight plus about one turn while holding the valve body. Restore the water slowly and check for leaks.
What you need
- A 15mm compression isolating valve, such as the 15mm chrome isolating valve, the angled version for tight corners, or a full bore valve for showers and higher flow.
- Or an isolating flexible tap connector to isolate and connect a tap in one part.
- A pipe cutter or junior hacksaw, deburring tool, two spanners, a tape measure and a marker.
- Spare olives, a towel and a bowl.
See all options in isolation and service valves and valves.
Step by step
- Turn off the water. Close the stopcock (or the gate valve on a tank-fed pipe) and open the nearest taps to drain the pipe.
- Choose the spot. Pick a straight, accessible length of pipe where the valve can be reached and turned with a screwdriver.
- Measure and mark. Hold the valve against the pipe. Mark the cut so the pipe will go fully into both ends of the valve. Most isolating valve bodies need a cut slightly shorter than the overall valve length.
- Cut and deburr. Cut the pipe square with a pipe cutter, catch the water, and remove any burrs. The pipe ends must be round and clean.
- Fit nuts and olives. Slide a nut and then an olive onto each pipe end.
- Fit the valve. Spring the pipe ends into the valve, making sure both go fully home. If the valve has a flow arrow, point it in the direction the water flows.
- Tighten. Hand-tighten both nuts, then hold the valve body with one spanner and turn each nut about one more full turn with the other.
- Test. Close the valve (slot across the pipe), turn the water back on slowly, check for leaks, then open the valve (slot in line with the pipe) and check again.
Tips
- A screwdriver-slot isolating valve is open when the slot lines up with the pipe, and closed when it is across the pipe.
- Turn valves occasionally so they don't seize.
- If a joint weeps, nip the nut up a little more. See how to fix a leaking compression fitting.
- Do not fit or alter valves on gas pipework. That is work for a Gas Safe registered engineer.
Need help choosing? Read how to choose radiator and isolating valves.
FAQs
Which way is an isolating valve open?
On a slotted isolating valve, the slot in line with the pipe means open, and the slot across the pipe means closed.
Do isolating valves need PTFE tape?
Not on the compression joints. They seal on the olives. Tape is only for threaded connections.
Can I fit an isolating valve without draining the system?
You need to turn off the supply and drain the section of pipe you are cutting. On a mains cold pipe, closing the stopcock and opening a tap downstairs is usually enough.
Where should isolating valves go?
On the supply to each tap, toilet cistern, washing machine, dishwasher and shower feed, so each can be serviced without turning off the whole house.