Fuse box replacement is one of those jobs that gets recommended a lot, and not always for the right reasons. Some old consumer units genuinely need replacing. Others are flagged on an EICR as an improvement recommendation, which is meaningfully different from a dangerous condition requiring urgent action.
This guide cuts through that. It explains what an old fuse box actually is, the signs that replacement is genuinely necessary versus advisable, what the job involves, and what it costs in London in 2026.
If you are trying to decide whether to act now or wait, this should give you a clear answer.
The terms are used interchangeably, but they refer to different generations of the same thing.
An old-style fuse box contains rewirable fuses or cartridge fuses. When a circuit overloads or faults, the fuse wire melts, or the cartridge blows, cutting power. To restore it, you replace the wire or cartridge.
These boards, many of which were manufactured by Wylex and installed in UK homes from the 1950s through to the 1980s, have no RCD protection. They protect the wiring from overload, but they do not protect people from electric shock caused by a fault to earth.
A consumer unit is the modern equivalent. It contains MCBs (miniature circuit breakers) that trip and reset with a switch, and either an RCD or individual RCBOs that cut power within milliseconds if current leaks to earth. This combination protects both the wiring and the people using it.
The key distinction matters because an old fuse box that works is not automatically dangerous, but it also does not provide the level of protection a modern installation would.
Where it becomes a genuine concern is when the lack of RCD protection combines with other risk factors: old wiring, a wet environment, high-demand circuits, or a rental property with legal compliance requirements.
There is a difference between a consumer unit that is old and one that is unsafe or non-compliant in a way that requires action. Here is how to read the difference.
If your fuse box requires you to thread new fuse wire when a circuit fails, it is a rewirable board. These boards have no RCD protection and no MCBs, and they will not trip instantly in a fault condition. They rely on the fuse wire melting, which takes longer and provides less protection.
On an EICR, the absence of RCD protection on a rewirable board is typically coded C3 (improvement recommended) unless the specific circuits involved push it to C2 (potentially dangerous).
The practical implication: rewirable fuse boards should be replaced. Whether that is urgent or can wait for a planned renovation depends on the rest of the installation and the use of the property.
An Electrical Installation Condition Report grades defects across four codes.
If the consumer unit itself has received a C1 or C2 code, replacement is not optional. For rental properties in England, C1 and C2 defects must be remediated within 28 days of the EICR under the Electrical Safety Standards in the Private Rented Sector Regulations 2020.
Failure to do so can result in fines of up to £30,000.
Old consumer units positioned in bathrooms, utility rooms, or any location with significant moisture exposure are a specific risk. Modern consumer units must be housed in appropriate enclosures and away from water sources. An old bakelite or open-backed fuse board in a damp environment is a combination that an electrician should be asked to look at promptly.
An MCB that trips repeatedly and will not hold a reset, or an RCD that nuisance-trips across multiple circuits, can indicate a failing device rather than an underlying circuit fault.
A consumer unit where individual devices are failing is a reasonable candidate for replacement rather than piecemeal repair, particularly on older boards where parts are increasingly difficult to source.
Scorch marks around fuse holders, a persistent burning smell from the consumer unit, or a board that feels warm to the touch are all indicators of a serious problem.
These are not situations to monitor. They require an electrician to investigate immediately, and in most cases, replacement will follow.
This is not a safety trigger, but it is a practical one. A visible old rewirable fuse board will be flagged by any competent surveyor or EICR inspector.
For rental properties, the compliance obligation is legal. For a sale, an old fuse board without RCD protection will often appear in a buyer's survey and become a price negotiation point. Replacing it before marketing can avoid that conversation entirely.
A fuse box installed when a property had five circuits and a single television is not necessarily adequate for a home that now has an EV charger, underfloor heating, multiple home office circuits, and a hot tub.
If the existing board is at capacity or has had circuits added in a way that does not match the original design, an upgrade is the right response rather than continuing to patch around it.
An electrician who tells you a fuse box needs replacing is not always wrong. But they should be able to explain why.
A consumer unit that has been installed within the last 15 to 20 years, contains RCD or RCBO protection, has no C1 or C2 codes on a recent EICR, and is operating without issues does not need replacing.
An EICR that returns only C3 observations (improvement recommended, not immediately dangerous) does not require urgent action. However, the observations should be kept on file and addressed over time.
If an electrician tells you the consumer unit must be replaced based on its age alone, or without producing an EICR or explaining which specific defect makes replacement necessary, that is worth questioning.
The job typically takes between four and eight hours for a standard domestic property, longer for larger installations or where remedial wiring work is identified during testing. The process goes something like this:
On completion, the electrician issues an Electrical Installation Certificate (EIC), which is the legal record of the work under Part P of the Building Regulations.
During testing, the electrician may identify wiring faults or deficiencies that need to be addressed before the new unit can be certified. This is more common in older properties and is the main reason costs can exceed the original estimate.
A property with clean, compliant wiring installs quickly. One with old rubber-insulated cables or incorrectly earthed circuits takes longer and costs more.
The job is notifiable under Part P, which means it must be carried out by a registered electrician or notified to the local building control authority. All competent person scheme members: NICEIC, NAPIT, ELECSA, can self-certify the work.
Fuse box replacement is consistently more expensive in London than the rest of the UK, for the same reasons as any other electrical work: higher operating costs, congestion charges, parking, and London labour rates.
All prices include labour, materials, testing, and the Electrical Installation Certificate. VAT should be confirmed with your contractor.
The difference between a dual RCD board and a full RCBO board is worth understanding. A dual RCD board splits your circuits into two groups, each protected by one RCD. If a fault on any circuit in a group trips the RCD, all circuits in that group lose power.
A full RCBO board gives every circuit its own individual protection, so a fault only cuts the one circuit affected. RCBO boards cost more, but the practical benefit of not losing half your property's power over a single faulty appliance is significant for most households.
A straightforward swap on a well-maintained property comes in at the lower end of these ranges. Several factors push it higher.
Old or non-compliant wiring: If testing reveals cables that cannot be safely connected to a modern consumer unit (rubber-insulated conductors, improperly earthed circuits, cables that lack sleeving) those need to be addressed before the new unit can be certified. This adds both time and cost.
Relocating the consumer unit: Moving the board more than a short distance from its existing position requires extending the meter tails, which may need to be done in coordination with the distribution network operator. This adds time, materials, and sometimes a second visit.
Three-phase supply: Commercial properties and some larger domestic installations with three-phase supplies require a more complex consumer unit and more circuits to test.
Central London location: Congestion charges, parking restrictions, and travel time in central London postcodes add to any contractor's overheads and are reflected in the quote.
Fuse box replacement is necessary when the existing unit presents a genuine safety risk, fails a compliance inspection with a C1 or C2 code, or cannot adequately protect a modern electrical installation. It is advisable when the board is old and lacks RCD protection, even if it is still functioning. It is not always urgent just because a board is dated.
The right starting point, if you are unsure, is an EICR. A thorough inspection will tell you the condition of the entire installation, code any defects accurately, and give you a clear basis for deciding whether replacement is needed now, soon, or can wait.
If you need an EICR or an electrician to assess whether your consumer unit needs replacing — whether for a residential property, a rental portfolio, or a commercial site — FS Group covers London and the South East. Call us on 0800 689 3497 or get in touch online.
