Overflow pipe is gushing water

It’s always worrying when an overflow pipe is gushing water. It’s a common problem but is luckily easily fixed. The overflow does two jobs. The first is to carry excess water outside and the second is to warn you that something has gone wrong.

Overflow pipe gushing water
Overflow pipe gushing water

To initially stop the pipe overflowing you should turn off the water. This is normally done at one of three places.

  1. Stopcock inside the house- normally under the kitchen sink or in a bathroom but can be almost anywhere on the ground floor.
  2. The stopcock outside the house – normally in the path under a plastic or metal cover.
  3. The isolation valve on the pipework going to the leaking valve. Some have valves most don’t. The isolation valves tend to leak if you use them so it can cause more trouble.

The most common fault is a stuck ball valve in a tank in the loft/attic. Ball valves are used to automatically turn off the water supply when a tank is full. If they develop a fault the water can continue to flow even when the level is too high causing the overflow to gush water.

To find where the fault is follow the pipe back to where it comes from.


If the pipe comes from the eaves (near the roof) you will need to check in the loft to look at the tanks in there.

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If the pipe comes from near a toilet you need to look in the toilet cistern to see the water level in there.

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Follow the pipe to see where it comes from. It could from an overflowing toilet, hot water tank in the bathroom or a boiler located in a bathroom cupboard.

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Metal pipe near a boiler

This is normally the pressure relief pipe from a sealed central heating system.

Boiler safety pipe dripping for long time.

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Metal pipe from a hot water tank

This is normally the safety pipework from an unvented tank.

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Metal pipe from the eaves

This is normally the overflow from a solid fuel hot water system.

This is usually similar to a normal hot water system except made from metal to deal with the extra heat that can be created by coal or wood fires. When gas or oil boilers get too hot they turn themselves off. Solid fuel can’t practically be turned off so can very easily overheat.

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