How do I fix a bath that leaks only when it is full?

A bath waste kit is two connections: the plug hole, which is wet whenever the bath is used, and the overflow, which is only wet when the water is high. That difference is what makes this diagnosis reliable.

What you'll need

• A torch
• A bowl and cloths
• A replacement overflow seal or waste kit
• Grips or a screwdriver

Step by step

1. Confirm the pattern.Fill the bath to normal depth and check underneath. Then fill it to just below the overflow and check again. A leak that only appears at the higher level is the overflow.
2. Remove the panel and dry everything.Wipe the whole waste assembly and the floor dry, then put dry paper down. It makes a small leak obvious rather than ambiguous.
3. Fill and watch with a torch.Fill towards the overflow and watch the overflow plate, the flexible pipe and both ends of it. Water tracking along a pipe can appear a long way from where it starts.
4. Check the overflow plate seal.The chrome plate inside the bath is held by a screw through to the elbow behind. Between them is a rubber or fibre washer that hardens and shrinks with age.
5. Tighten the plate gently first.Sometimes the screw has simply worked loose. Nip it up and retest before dismantling anything.
6. Replace the seal if tightening does not hold.Undo the centre screw, take the plate off, fit a new washer or a ring of silicone, and reassemble. Do not overtighten against acrylic.
7. Check the flexible overflow pipe.It runs from the overflow elbow down to the waste trap. It splits at the bends, and its push-fit or screwed ends work loose. Replace it if it is cracked.
8. Check the waste at the same time.While you are there, refit the waste's washers if they look hard, and check the trap connection is not weeping — a full bath puts more head on all of them.
9. Retest properly.Fill right up to the overflow and let some water run through it. That is the only test that proves the repair.
10. Check what the leak has already damaged.A slow overflow leak wets the floor under the bath for months. Check the deck and the ceiling below before closing the panel up.

Tips

• Fill in stages and check between each. It tells you the height at which the leak starts, which usually identifies the part.
• If the overflow pipe is a rigid old-style one, a modern flexible replacement kit is easier to fit in a tight space.
• Dry paper on the floor under the waste is a far better leak detector than looking for wet.

Common mistakes

• Assuming any bath leak is the waste — The waste is wet on every use, so a waste leak shows every time. A leak that only appears on a full bath has to be the overflow, and replacing waste washers achieves nothing.
• Overtightening the overflow plate screw — It pulls the plate hard against thin acrylic and can crack it, and it distorts the seal so it leaks worse.

If it doesn't work

Questions people ask