How to Replace a Consumer Unit
Last updated: 7 September 2026
Consumer unit replacement must be done by a qualified electrician and requires notification under Building Regulations.
Overview
Replacing a consumer unit is a major electrical job. This guide covers the process and when to call a professional.
Step-by-Step Fix
Before beginning any repair, ensure you have isolated power or water supplies. Clear your workspace, gather standard hand tools, and wear appropriate personal protective equipment (PPE).
- A consumer unit replacement is a complex job that requires isolation of the supply, removal of the old unit, and installation of a new one with RCD protection.
- The process involves disconnecting all circuit cables from the old unit, fitting a new backplate, mounting the new consumer unit, and reconnecting the circuits.
- All connections must be torqued to the manufacturers specifications. Each circuit must be tested for insulation resistance, continuity, and correct polarity.
- The installation must comply with BS 7671 (IET Wiring Regulations) and must be notified to Building Control under Part P of the Building Regulations.
- Only a qualified electrician registered with a competent person scheme (such as NICEIC or NAPIT) should carry out this work.
- Before starting the work, the electrician will carry out a pre-work inspection to identify any issues that may affect the installation.
- After installation, the electrician will issue an Electrical Installation Certificate (EIC) and notify Building Control of the work.
- The old consumer unit should be disposed of responsibly, following local regulations for waste electrical and electronic equipment.
Common Symptoms & Diagnostic Resolutions
Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.
| Symptom / Code | Likely Root Cause | Recommended Resolution |
|---|---|---|
| No power | Installation error | Check all connections and circuit breakers. If you have no power after installation, contact your electrician immediately. |
| RCD tripping | Earth fault or wiring issue | Check circuit insulation and connections. If the RCD trips, there may be a fault in one of the circuits that needs to be identified and rectified. |
| MCB not holding | Faulty MCB or circuit fault | Check the circuit for faults. If the MCB will not hold, there may be a short circuit or overload on the circuit. |
| Lights dimming | Voltage drop or loose connection | Check all connections and the supply voltage. If lights dim when appliances are switched on, there may be a loose connection or undersized cable. |
Frequently Asked Questions
Do I need a new consumer unit?
If your consumer unit is over 20 years old or does not have RCD protection, it should be replaced. Modern consumer units with RCD protection are much safer than older units. An electrician can advise you on whether your consumer unit needs replacing.
How much does a consumer unit replacement cost?
Typically £400-£800 depending on the size and complexity of the installation. The cost includes labour, materials, and testing. It is advisable to get quotes from at least three electricians before proceeding.
Can I replace a consumer unit myself?
No, replacing a consumer unit is notifiable under building regulations and must be carried out by a qualified electrician. Attempting to replace a consumer unit yourself is dangerous and illegal.
How long does it take to replace a consumer unit?
Typically 4-8 hours, depending on the size of the installation and the complexity of the work. If the existing wiring is old or in poor condition, the work may take longer as the electrician will need to test and rectify any issues.