Electric shower replacement

For most homeowners, a "like-for-like" replacement is straightforward, but upgrading to a higher kilowatt (kW) rating often requires significant wiring changes. This guide breaks down the costs, regulations, and technical requirements to ensure your new shower is both safe and legal.

What Does the Work Involve?

• Isolation and Verification: The electrician will safely isolate the power at the consumer unit and use a voltage tester to ensure the circuit is dead before removing the cover.
• Decommissioning: The existing unit is disconnected from the mains water and electrical supply, then removed from the wall.
• Inspection: A crucial step where the electrician checks the existing cable size (e.g., 6mm² vs 10mm²) and the condition of the pull-cord isolator switch.
• Installation: The new unit is mounted, leveled, and connected to the internal pipework and wiring terminals.
• Commissioning: The shower is run on a cold setting first to bleed air from the system, preventing damage to the heating element.
• Testing and Certification: Final electrical tests are carried out to ensure the RCD (Residual Current Device) trips correctly and the earthing is sufficient.

Typical Costs

The total cost is primarily driven by whether your existing wiring can support the new shower. If you move from an 8.5kW shower to a 10.5kW model, your existing 6mm² cable may overheat, necessitating a full rewire of that circuit back to the consumer unit.

Pro Tip: Always check the "entry points" of a new shower. Choosing a model with similar water and cable entry positions to your old one can save an hour of labour and prevent unnecessary holes in your tiles.

How Long Does It Take?

• Like-for-like swap: 1–3 hours. This assumes the plumbing and wiring line up perfectly and the cable is adequate.
• Upgrade with new cable run: 4–6 hours. This involves fishing new 10mm² cable from the consumer unit to the bathroom, which may involve lifting floorboards.
• Full installation (New circuit): 1 day. This includes installing a new breaker, running cable, fitting the isolator, and the shower unit itself.

DIY or Professional?

While a DIYer might feel confident swapping a unit, electric showers are high-load appliances located in "Special Locations" (bathrooms) as defined by UK law. Under Part P of the Building Regulations, any new circuit or significant alteration in a bathroom must be certified.

An electrician doesn't just "wire it in"; they verify that your earthing and bonding are up to modern standards. If you do it yourself and a fault occurs, your home insurance may be void, and you risk a serious electrical fire or shock.

Choosing the Right Tradesperson

• Check Registration: Ensure they are registered with a government-approved scheme like NICEIC, NAPIT, or ELECSA.
• Ask about Certification: Confirm they will provide a Minor Electrical Works Certificate upon completion.
• Look for Red Flags: Avoid anyone who says the RCD "isn't really necessary" or who refuses to check the cable thickness.
• Questions to Ask:
  • Is my current consumer unit compliant with the 18th Edition Wiring Regs?
  • Will you need to lift floorboards to check the cable?
  • Is the price inclusive of VAT and the cost of the unit?

UK Regulations

• BS 7671 (Wiring Regulations): All work must meet the current 18th Edition standards for safety and installation.
• Part P (Building Regulations): Most bathroom electrical work is "notifiable" to local building control or must be self-certified by a registered pro.
• RCD Protection: All modern electric shower installations must be protected by a 30mA RCD to prevent fatal shocks.
• Isolation: A double-pole isolation switch (usually a ceiling pull-cord) must be present outside the "zones" or within reach for safety maintenance.

Common Problems

• Undersized Cables: Using a 10.5kW shower on an old 6mm² cable is a major fire hazard. The cable will get hot enough to melt insulation over time.
• Burnt-out Switches: Pull-cord switches are a common failure point; if the connections aren't tightened to the correct torque, they will arc and burn out.
• Limescale Build-up: In hard water areas, old showers fail because the heating element scales up, causing the "Pressure Relief Device" (PRD) to blow.
• Inadequate Pressure: Electric showers require a minimum "running pressure" (usually 1 bar). If your mains pressure is low, the shower will cycle between hot and cold.

Frequently Asked Questions

Can I replace an 8.5kW shower with a 10.5kW model?

Only if your wiring and fuse/circuit breaker are rated for the higher load. A 10.5kW shower draws about 45 Amps, which usually requires a 10mm² cable. Your electrician will check this before starting.

Do I need a plumber or an electrician?

While some plumbers can do basic swaps, an electrician is generally preferred. They can certify the electrical safety and handle any necessary upgrades to your consumer unit or wiring.

Why is my shower pull-cord switch getting hot?

This is a sign of a loose connection or an overloaded switch. It is a fire risk and should be inspected by a professional immediately. Do not use the shower until it is fixed.

How long should an electric shower last?

Most units last between 7 and 10 years. In hard water areas, this lifespan can be shorter due to limescale build-up on the heating elements.

Does the shower need its own fuse in the consumer unit?

Yes. An electric shower must be on its own dedicated circuit, never spurred off a ring main or lighting circuit, due to the high amount of current it draws.

What is a Minor Electrical Works Certificate?

It is a formal document issued by your electrician confirming that the work was tested and meets UK safety standards. You should keep this for your records, especially if you sell your home.