The free diy home improvement guide with answers to your questions on a wide range of do it yourself projects.


Service Valve – Repair or Replace a Leaking Valve

Service valves are used to isolate sections of the plumbing system to allow for repair and maintenance. Knowing how to repair or replace a valve will save you money and get you out of trouble in an emergency.

There are many different valves used in domestic plumbing including gate valves and ball or isolation valves. Gate valves are commonly found on the cold water pipe coming from the cold water storage cistern in the loft. Isolation valves are commonly found on pipe work going to appliances such as washing machines and wc cisterns.

In order to carry out work on one of these valves you will need to switch off the water and drain down the appropriate section of plumbing. See Turning Off The Water and Draining Down Sealed Central Heating System or Draining Down Vented Central Heating System

Leaking Gate Valve or Isolation valve

There are two common examples of leaking valves. There may be water leaking from the spindle on a gate valve or, on both gate valves and isolation valves, there may be a leak from the compression nut where the valve is connected to the pipe work.

Leaks from gland nuts – the small nut at the base of the spindle – can often be resolved by tightening the nut a little. To do this, you should hold the body of the valve with a wrench to prevent it moving, then use a spanner or second wrench to tighten the nut. If this fails to stop the leak, you may need to repack the gland nut, or simply replace the valve.

Where there’s a leak on one of the joints with the pipe work, you can sometimes cure this by nipping it up a little. Again holding the valve with a wrench to prevent it twisting and making the leak worse, use a second pipe wrench to tighten the compression nut a little. Don’t overdo it though as excess tightening can damage the olive and make the matter a lot worse.

Replacing a Service Valve

If the leak cannot be stopped, you will need to refit the valve or if the valve has seized altogether, you will need to fit a replacement. When buying a replacement, buy one that is the same size so that you won’t have to make any changes to the pipe work. Some valves are directional so before removing the old one, make a note of the direction of flow so that you can fit the new one the same way round.

Undoing the Valve

You will need two pipe wrenches or a wrench and a spanner to suit the size of the compression nut . Hold the body of the valve to prevent it twisting and exerting pressure on the pipe work. Use the second wrench, or spanner, to undo the compression nut. Repeat this on the other end of the valve and gently ease the valve away from the pipe work. The fitting is often quite tight as the pipe sits inside the valve at both ends and there’s not much play.

With the valve removed, you now need to take the olives – rings mounted over the pipe work – off the pipes. Olives are squashed tight against the pipe in a compression fitting so they may be difficult to remove. The first option is to use a gentle grip with a wrench and rotate them a little as you pull them off the pipe. If this doesn’t work you’ll need to cut them off. Use a junior hacksaw and cut through the olive at an angle being careful not to cut or damage the pipe at all. Finally, clean up the pipe ends using a wad of steel wool.

Fitting the New Valve

Hold the new valve next to the pipe work to ensure that no adjustments are needed and that the pipe both sides will sit into the valve the correct amount. If you look inside the end of the valve you’ll see an edge where the pipe should stop.

Slide the compression nut onto the pipe followed by the olive and do the same for the other end. Fit the valve onto the pipe work – this may require a little work as there’s often not much play in the pipe work. With the valve in position, double check the flow direction.

Hand tighten the compression nut on both ends. Hold the body of the valve with a wrench to stop it turning and then tighten the nut at either end. This tightening process compresses the olive around the pipe to form the seal. When the nut feels moderately tight, give another half turn to fully tighten but don’t overdo it. Remember, you can always nip it up a bit but if it’s over tightened you’ll be back to square one. Sometimes a poorly fitting joint can be sealed by wrapping PTFE tape around the olive to improve the seal – note, PTFE tape isn’t used around the threaded section.

Switching the Water On

With the valve in the closed position, turn the water back on and inspect your work for leaks. If all looks ok, open the valve and check again. Once you’re happy you’ve done a good job, make sure all supplies are working properly and that there are no air locks in the pipe work.

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