Inspired by a UK plumbing tutorial. This article draws on the method shown in the How To Change Single Bath Taps To Mixer Bath Tap With Shower Attachment video from a UK plumber on YouTube. Practical and to the point, covering the basin spanner access and the tail connector connections that catch most people out.
1. Check your water system first
A standard bath shower mixer works best with balanced hot and cold pressures — both supplies at the same pressure. Combi boiler systems are generally fine. If your cold supply comes direct from the rising main and your hot from a vented cylinder, the pressures will be unbalanced and the shower will run poorly.
In that case, look for a pressure-compensating shower mixer or add a separate cold supply from the cold water tank rather than the mains. It is worth sorting this before buying the tap.
2. Isolate the water supply
Turn off the hot and cold isolation valves under the bath, or close the gate valves on the supply pipes. If there are none, shut off at the mains stopcock and the hot water cylinder draw-off. Open the taps to drain the pipes before disconnecting anything.
Lay an old towel in the bath to catch any drips and protect the enamel while you work.
3. Remove the old taps
Access under the bath is usually tight. A basin spanner — a long-handled wrench with a swivelling head — is more or less essential for reaching the backnut that holds each tap to the bath deck. Undo the backnut, remove the tap, and pull out the old supply pipes.
Clean up any old silicone or putty from the tap hole surface before fitting the new tap. A flat surface helps the seal bed properly.
4. Check the hole size and centres
Most UK baths have two tap holes at 180 mm centres, although some older baths are at 203 mm. Measure your bath and check the mixer you are buying matches. A mixer tap designed for 180 mm centres will not sit flat on a wider-hole bath without adapter plates.
If you only have one hole — a monobloc layout — you will need a monobloc bath shower mixer, which is a different product. Worth double-checking before you get to the shop.
5. Fit the new mixer tap
Pass the mixer body up through the tap holes from below. Most deck-mounted mixers include a rubber or plastic deck plate to bridge the holes and a backing plate for under the bath. Feed the hot and cold tails down through the holes, then thread on the backnuts and tighten with the basin spanner.
Finger-tight plus a quarter-turn with the spanner is enough. Over-tightening deforms the rubber seal and leads to drips — and getting back under the bath to redo it is not a pleasant way to spend an afternoon.
6. Connect the supply pipes
Most modern mixer taps come with flexible tap connectors — 15 mm push-fit or compression fittings to the hot and cold tails. Connect hot to hot and cold to cold. The tails are usually labelled, but if not, the convention in the UK is hot on the left, cold on the right when facing the tap.
Use PTFE tape on any threaded connections. Two or three turns on male threads, wound in the direction of the thread, is enough.
7. Fit the shower handset and slide rail
Mark the wall for the slide rail and drill for the appropriate fixings — plastic plugs in a tiled wall, using a tile bit to start the hole. Fit the rail bracket, clip the rail in, and hang the handset holder at a comfortable height.
Connect the flexible shower hose to the mixer outlet. Most are a standard 1/2 inch BSP thread. Hand-tighten only — no tools needed and no PTFE tape required on rubber-washer connections.
8. Turn on and check for leaks
Open the isolation valves slowly and watch each connection under the bath as the pressure builds. Run the tap through its full range — cold only, hot only, mixed — and check the hose connection at both ends while the water is running.
If there is a thermostat or temperature limiter on the mixer, adjust it with the small screw on the cartridge head, following the manufacturer's instructions. Set it to around 38°C for comfortable showering without scalding risk.
When to call a handyman
Call Richard if there are no isolation valves and the mains needs isolating, if the existing supply pipes need extending to reach the new tap, or if the bath panel access is awkward. Fitting a bath mixer is well within most people's abilities — but access under older baths can be genuinely difficult without the right tools.
Need a bath tap or shower mixer fitted?
The Sandwich Handyman fits bath taps, shower mixers, and general plumbing fittings for homes in Sandwich and around the area.
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