Find and fix a leak under a bath

Find and fix a common bath leak by checking sealant, waste, tap and pipe connections in one session.

LB-01Gather your tools and dust sheetsLay an old towel or dust sheet in the bath and on the floor beside it. You will need a torch, adjustable spanner, sealant gun, mastic removal tool, cloths and a bright light, since most of this job is done lying down looking under the bath edge or through the access panel.

1 each · Torch or head torch

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1 each · Adjustable spanner

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4 each · Microfibre cloths

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LB-02Turn off the water supplyFind your stopcock, usually under the kitchen sink, and turn it clockwise to shut off the water. Run the bath cold tap briefly to check the supply has actually stopped before you start work.

LB-03Remove the bath panelMost panels clip onto plastic legs, or are held with a few screws along the bottom edge. Undo the screws or pop the clips gently, then lift the panel away and set it aside somewhere it will not get trodden on.

1 each · Screwdriver (matching panel screws)

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LB-04Dry everything and run the water to spot the leakWipe every pipe joint, the underside of the bath, and the floor dry with a cloth. Get someone to run the bath taps and the shower (if fitted) for a minute while you watch closely with the torch, looking for the first drip rather than the pooled water.

LB-05Check the sealant line around the bath edgeA cracked or missing silicone seal where the bath meets the wall or floor tiles is the most common cause. If it is cracked, peeling, or you can see daylight through it, cut it out with a mastic removal tool, clean the gap with methylated spirit, let it dry fully, then run a new bead of silicone sealant and smooth it with a wet finger.

1 each · Bathroom silicone sealant cartridge

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1 each · Mastic removal tool

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1 bottle · Methylated spirit

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LB-06Check the waste trap and overflow connectionsLook at the plastic waste trap under the bath and the overflow pipe. Hand-tighten any loose compression nuts, and check for a cracked trap body, which will need replacing whole rather than sealing. Wrap PTFE tape around any threaded joint you undo before doing it back up.

1 roll · PTFE tape

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1 each · Replacement bath waste trap (if cracked)

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LB-07Check the tap tails and mixer connectionsFeel around the tap tails under the bath where the pipework connects. If there is a slow drip from a compression joint, tighten it a quarter turn with the spanner. If a fibre washer inside the joint looks perished, undo the nut, fit a new washer, and do it back up firmly but not over-tight.

1 pack · Plumbers' fibre washer set

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LB-08Lift flooring nearby if the source is still hiddenIf water is tracking from further away, you may need to lift a floorboard or access hatch to follow the pipe run. Cables and pipes can run almost anywhere under a floor, so use a cable and pipe detector first, and still assume something is there until you prove otherwise by lifting carefully and looking. If there is any doubt, isolate the electrics at the consumer unit before cutting or lifting boards, and make sure the water is off at the stopcock before disturbing any pipework.

1 each · Cable and pipe detector

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1 each · Floorboard saw

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LB-09Test the repair before closing anything upTurn the water back on at the stopcock and refill the bath fully, then let it stand for 15 to 20 minutes. Check every joint and the sealant line again with dry cloths underneath, and only move on once you see no fresh damp patches.

LB-10Refit the panel and tidy upOnce you are confident the leak is fixed, refit the bath panel and its screws or clips. Let any new silicone cure for the time stated on the tube, usually 24 hours, before using the bath again, and dispose of old sealant offcuts and cloths.

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