Knowing how to change a ball valve is probably one of the most useful DIY skills you can have. If you’ve got a leaking or dripping overflow pipe, having this skill can save you a fortune from an emergency plumber call out.
How to change a ball valve on a loft tank
Isolate the cistern
Shut off the water supply to the ball valve you’re replacing. Ideally, there will be an isolation valve that you can turn with a blade-edge screwdriver. If there isn’t one, you’ll have to turn off the mains.
Loosen the valve
Hold the nut of the valve that’s on the inside of the cistern with a pair of adjustable spanners, and the body of the valve with a pair of grips. Loosen the nut with the spanner.
Change a ball valve – remove the old valve
While holding the valve body with your hand, use your other hand to unscrew the nut. Keep your fingers around the edge of the valve, ready to catch the washer so it doesn’t fall in the tank.
Prepare the valve
Using your adjustable spanner, unscrew the body of the new valve from its stem. Most valves come with a white high pressure nozzle and a red low pressure nozzle. For tanks fed by the mains, make sure that the white nozzle is fitted, and that the washer is there too. Remove the small plastic spout from the top of the valve
Change a ball valve – fit the new valve
While taking care not to drop the washer into the tank, screw the new valve in place. Make sure its arm is nice and straight with the surface of the water, and that the hole in the valve is at the top.
Tighten it up
Use your grips and adjustable spanner to tighten the valve up. Once it’s tight, reattach the small white plastic spout to the valve, and screw the float back on. You can of course use the float of the previous valve, as long as it’s still watertight. Give it a shake to check if there’s water inside.
Test the valve
Turn the water supply to the valve back on. If water doesn’t flow, gently push down on the float to open the valve. Observe that the valve shuts off properly, and that there are also no leaks from where you fitted the valve.
Set the correct water level
If necessary, adjust the level of the float so that the water level is 50 – 75mm below the overflow pipe outlet. Use a spanner to make sure that the nut on the float arm is really tight.
In the feed and expansion cistern, there must be enough room to accommodate the expansion of the water by approximately 4% of its original volume. This means that, when cold, the water level should only be a few centimetres above the outlet.