Is replacing an electric shower notifiable under Part P?

Yes. A bathroom is a special location under BS 7671 Section 701, and any electrical work in a bathroom is notifiable under Part P of the Building Regulations. Even a like-for-like shower replacement must be carried out by a registered electrician who can self-certify the work, or it must be notified to Building Control. If in doubt, hire a registered electrician: it is not expensive and you get a Minor Works Certificate for the property file.

What cable size does an electric shower need in the UK?

The cable size depends on the shower's power rating. An 8.5 kW shower typically uses 6 mm two-core and earth with a 40A MCB. A 9.5 kW or 10.5 kW shower needs 10 mm cable with a 45A MCB. Always check the manufacturer's installation instructions for the specific model you are fitting. If the existing cable is undersized for the new shower, the circuit must be upgraded before installation.

Can I fit a higher-kW shower on the existing circuit?

Only if the existing circuit cable and MCB are rated for the new shower. Fitting a 10.5 kW shower on a circuit wired in 6 mm cable with a 40A MCB is not safe: the cable will overheat under load. Check the MCB rating at the consumer unit and the cable size before buying a replacement shower, and contact an electrician if any circuit work is needed.

What is the pull-cord switch for on an electric shower circuit?

BS 7671 Section 701 requires that fixed electrical equipment in bathroom zones is controlled by a device outside the bathroom, or by a ceiling-mounted pull-cord switch that a person in the shower cannot reach while standing under the water. The pull-cord switch is a double-pole device that breaks both line and neutral -- it is not the same as the MCB at the consumer unit, and you should not work on the shower until both the MCB and the pull-cord are off.

How do I know which zone my shower unit is in?

BS 7671 defines bathroom zones based on distance from the shower head and water taps. Zone 1 is the area directly under the shower spray and above a bath. Most wall-mounted electric shower units are in Zone 1 or on the Zone 1 boundary. Equipment in Zone 1 requires a minimum of IPX4 (splash-proof) protection, which all UK domestic electric showers provide. The key restriction for Zone 1 is that only SELV (very low voltage) or wired-in appliances rated for the zone are permitted there.

How to Replace an Electric Shower Safely (UK)

Helpful video reference. "How To Install Mira Sprint Dual Outlet Electric Shower" is from the Toolstation YouTube channel. Toolstation is a UK trade and DIY retailer and the video follows the step-by-step installation of a Mira Sprint, one of the UK's best-selling domestic electric showers, covering the wall fixing, cold water connection, cable entry and terminal block connections throughout.

Before you start. Turn the shower circuit off at the consumer unit and lock it out. Turn off the cold water supply to the shower at the nearest stopcock. Test all conductors at the existing shower terminal block with an approved voltage tester before touching them. A bathroom is a special location: the combination of water and electricity makes this particularly unforgiving if you skip the dead test.

1. Isolate at the consumer unit and prove dead

Find the shower circuit MCB at the consumer unit, switch it off, and if possible lock it or tape over it so nobody turns it back on whilst you are working. Go to the bathroom ceiling pull-cord switch and switch that off too. Both devices must be off before you open the shower unit.

Inside the shower unit, test the line (brown), neutral (blue) and earth (green and yellow) terminals with an approved voltage tester before disconnecting anything. Confirm zero on all three. Do not rely on the pull-cord switch alone: an isolation tester showing dead at the pull-cord switch terminals is the only way to be sure.

2. Remove the old shower unit

Unscrew the shower body cover and take a clear photograph of the wiring inside before you disconnect anything. Note which terminal is line, which is neutral and which is earth. Loosen the terminals, pull the conductors free, and loosen the cable gland so the cable can be withdrawn from the unit.

Turn off the cold water supply (if you have not already), then disconnect the 15 mm cold water inlet pipe from the shower body. Most connections are compression fittings: unscrew the nut and withdraw the pipe, wrapping a cloth around the fitting to catch residual water. Unscrew the shower body from the wall and set it aside.

3. Check the existing circuit capacity

Before fitting the new shower, go to the consumer unit and note the MCB rating and the cable size running from it. The table below shows the common UK pairings:

7.5 kW or 8.5 kW shower: 6 mm two-core and earth, 40A MCB.
9.5 kW or 10.5 kW shower: 10 mm two-core and earth, 45A MCB.

If the new shower has a higher power rating than the old one, you may need to upgrade the cable and MCB before fitting it. That is an additional job for a registered electrician and must be certified separately. Fitting a more powerful shower on an undersized circuit is a fire risk.

4. Fix the new shower unit to the wall

Hold the new shower body against the wall in the same position as the old one, or choose a new position if you are moving it. Mark the fixing holes, drill at the correct diameter for the wall plugs, and fit wall plugs rated for the wall type (masonry plugs in a tiled wall, or toggle fixings if there is a stud behind the tile).

Thread the existing supply cable through the cable entry gland on the new unit before fixing the unit to the wall. Trying to thread the cable through afterwards, when the unit is screwed tight, is significantly harder. Leave enough cable inside the unit to reach the terminals with some slack.

5. Connect the cold water inlet

Connect the 15 mm cold water pipe to the shower unit's inlet fitting. Apply PTFE tape to any threaded connections and hand-tighten before finishing with a spanner, being careful not to over-tighten on plastic fittings. Turn the cold water supply back on slowly and check the connection is dry before closing up the shower unit.

Any water leak inside the shower unit enclosure creates a serious hazard once the power is restored. If there is any moisture inside, dry it out thoroughly before proceeding with the electrical connections.

6. Make the electrical connections and test

Strip each conductor to the length specified in the new shower's installation manual (typically 8 to 10 mm). Connect brown to the terminal marked L or Live, blue to N or Neutral, and green and yellow to the earth terminal. Tighten each terminal firmly: these conductors carry 40A or more and a loose connection will cause arcing and heat over time.

Fit and tighten the cable gland to grip the outer sheath of the cable, not the individual conductors. Refit the shower cover, restore power at the consumer unit and at the pull-cord switch, and test the shower on every power setting. Check for warm spots on the cable or fittings during the first few minutes of use: both suggest a poor connection that needs reopening.

Stop and call an electrician if: the cable inside the shower unit has rubber or cloth insulation rather than PVC (old wiring), the colours are red and black rather than brown and blue (pre-2004 wiring), there is no earth conductor, the MCB trips immediately on restoration of power, water has entered the cable, or you are fitting a shower with a higher kW rating than the old one and the circuit cable appears undersized.

When to call us

Richard replaces electric showers across Sandwich, Deal, Dover, Ramsgate and Canterbury, issuing a Minor Electrical Works Certificate on completion. If the job needs a circuit upgrade, that is done at the same visit. Small local jobs are charged at £10 per 10 minutes with no hidden call-out fee.

Need a shower replaced in Sandwich or east Kent?

Richard handles like-for-like shower replacements and full circuit upgrades. Minor Electrical Works Certificate provided on the day.

Contact Richard

How to replace an electric shower safely