Replace a bath shower mixer diverter

Isolate the water, remove the tap handle and spout, swap the worn diverter cartridge, then test for leaks.

BM-01Work out what type of diverter you haveBath shower mixers use two common diverter designs. Some have a pull-up rod or knob on the spout that lifts to send water up to the shower. Others have a small lever or dial next to the hot and cold handles, with a cartridge behind it. Run the bath tap and try the diverter now, so you know which parts to expect when you take the tap apart.

BM-02Buy the right replacement part and gather toolsTake a photo of the tap, or its make and model if visible, to a plumbers' merchant, since diverter cartridges and rods are not universal between brands. You'll need Allen keys, a flat or crosshead screwdriver, and an adjustable spanner. PTFE tape and a little silicone plumbers' grease make reassembly easier and help stop leaks.

1 each · Replacement diverter cartridge or rod kit

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1 set · Allen key set

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1 each · Adjustable spanner

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1 roll · PTFE tape

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1 tube · Silicone plumbers' grease

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BM-03Isolate the water supplyTurn off the isolation valves under the bath panel if your tap has them, or turn off your stopcock (usually under the kitchen sink) and check it turns fully. Open the bath hot and cold taps fully to drain water sitting in the pipes, and leave them open while you work.

BM-04Protect the bath and set up your work areaLay an old towel or dust sheet in the bottom of the bath to stop dropped tools chipping the enamel or acrylic. Keep a small bucket and cloth nearby to catch any drips when you disconnect parts.

1 each · Old towel or dust sheet

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1 each · Small bucket

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BM-05Remove the tap handle or spout to reach the diverterFor a pull-rod diverter, unscrew the small grub screw or cap on the spout with an Allen key, then pull the rod and diverter assembly straight out. For a lever-type diverter, prise off the decorative cap on the handle with a flat screwdriver, undo the screw underneath, lift the handle away, then unscrew the retaining collar or nut with the adjustable spanner to expose the cartridge.

BM-06Take out the old diverter and check the housingPull or unscrew the worn diverter cartridge or rod assembly out of the tap body. Wipe out the housing with a cloth and check for limescale or grit, since this is often why a diverter sticks or leaks. Lay the new part next to the old one to check they match before fitting.

BM-07Fit the new diverterSmear a thin layer of silicone plumbers' grease on the new part's rubber seals, then push or screw it into the housing the same way the old one came out. Wrap PTFE tape around any threaded collar before tightening it firmly by hand plus a light turn with the spanner. Do not over-tighten, as this can crack the tap body.

BM-08Reassemble the handle or spoutRefit the collar, handle or spout in reverse order, replacing the retaining screw and pressing the decorative cap back into place. Check the diverter moves freely by hand before turning the water back on.

BM-09Turn the water back on and test for leaksClose the bath taps, then turn the isolation valves or stopcock back on slowly. Run the bath tap, then operate the diverter to send water to the shower, checking the spout, handle and any joints for drips. Leave the water running for a couple of minutes and check again before you finish.

BM-10Tidy upDry the bath and surrounding tiles, and wipe down your tools before putting them away. Dispose of the old diverter part, and keep the box or model number in case you need to order a replacement again in future.

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