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Ball valve passing in tank

A ball valve passing in the tank means the valve has not closed properly. When the water reaches the set level, the tank continues to fill.

What does it mean if the ball valve is passing?

A ball valve is designed to fill a tank (technically a cistern). It should then stop filling when the water reaches the desired level.

If the ball valve is passing, the valve stays open after the water reaches the desired level.

a ball valve in a central heating header tank

How do I know my ball valve is passing?

The first sign a ball valve is “passing” is when water flows from the overflow pipe.

Follow the running overflow pipe back to the tank it connects to.

To be certain the valve is passing:

  • Reduce the level of water in the tank. This can be through running a hot water tap or by scooping out into a bucket. I wouldn’t recommend siphoning using a hose. The water in central heating systems can be pretty dirty and full of chemicals.
  • The ball valve should now open and refill the tank. The water level should be quite high on big water storage tanks and quite low on central heating header tanks.
  • The float of the ball valve should now rise with the water level and the water flow should stop.
  • Don’t touch the float while it is turning off the water supply. A slight touch can be enough to hide the fault.
  • The flow of water should completely stop. A trickle or a drip will be enough to overfill the tank given enough time.
a float operated ball valve

How do I replace my ball valve?

There are a number of kits available to replace the innards of a ball valve. Personally, I don’t bother with them. I always just replace the whole valve. The price isn’t that much different, and it saves future problems.

A new float valve is available here.

Find the right tank

Take the lid and insulation from the top of the tank. Look in and make sure you are changing the right valve.  It’s the right one if the water level is above the overflow level.

Turn off the water

Turn the water off to the valve.  Every float operated valve should have a small valve before it so the water can be turned off. This is generally done using a flat screwdriver.  If the valve isn’t there turn off the whole house using the stopcock.

Drain the pipework

Push the ball down to release the pressure in the pipework. This will also serve to reassure you that when you disconnect the pipework, no water is going to come out.

Empty the tank

Lower the level of the water in the tank. This can be by opening a hot water tap downstairs (for hot water feed tank). Or by scooping out into a bucket (from the central heating fill tank).

Remove the old valve

Using a set of pliers and a spanner hold onto the valve and turn the compression nut with the spanner.  Take all the way off and slide down the pipe a few inches.

Unfasten the two flat nuts holding the valve onto the wall of the tank. Then feed the valve into the tank and dispose of it.

Assemble and fit the new valve

On the new valve tighten all the nuts up on the body of the valve before its installed. Attach the ball float. Remember to secure the float by tightening up the screw. The float should be low enough that the water level is a few inches below the overflow level.  On the small central heating tank you may have to bend the arm of the valve. This is so the water level is lower in the tank. This gives space for the water level to rise when the heating is on.

Connect up the water supply

Screw one of the flat washers all the way down the thread of the valve.  Now push the threaded part of the valve through the hole in the tank.  There is normally a rigid rectangular piece of plastic to support the tank. Push this over the threaded part of the valve.  Now thread the second flat nut onto the valve and tighten up both nuts. This secures the valve to the tank with the spout on the top. The ball and arm should be free to move up and down.

Now look at the water supply pipe.  It will either have a nut and olive or a 1/2 inch tap connector with a washer.  If it is a nut and olive, push the pipe into the valve up to the olive and tighten up. Remember to hold the valve in the upright position with a spanner or grips.

If it is a tap connector and washer, dig the old washer out and replace it with a new one. Push the tap connector so it is sitting square on the threaded part of the valve. Tighten up the nut.  When threading the nut onto the valve be very careful to avoid cross-threading.  If it feels like it has gone tight a lot earlier than you expected stop and check. It may not have gone on the thread square.  Not checking this can ruin both the nut and the valve so it’s better to be cautious.

Turn the water back on

The only thing left is to turn the water back on.  Turn it on gently to start with so its easier to turn off if the joints leak.  If the joints outside the tank are sound let the tank fill up to its natural level.  Don’t turn off the water by pulling the float up.  This can give you a false reading about the water level. You may have to adjust the level of the float on the arm to give the right water level.

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