Consumer unit replacement cost and what's in the price.

What the replacement includes

Each circuit gets an RCBO of its own, which is a circuit breaker and an RCD in one. A fault on one socket circuit then trips that circuit alone, and the lights and the fridge stay on. Older split boards often put half the house behind a single RCD, so one fault takes all of it out.

Boards in homes have had to be non-combustible since the wiring regulations changed, after fire investigators reported more fires in consumer units with plastic cases. Most of those fires started at badly made connections, so the work inside counts for as much as the metal case.

A surge protector catches the voltage spikes that switching and lightning send down the cables, before they reach the electronics in the house. The wiring regulations expect one on a new board unless the owner declines it and accepts the risk of damage to their equipment.

An AFDD (arc fault detection device) cuts a circuit off when it senses arcing at a damaged cable or a loose connection. I fit them at a board change if you ask, and they're quoted on top.

If a car charger or a home battery might follow, mention it at the survey. Each one takes up a way on the board, and the new board can leave room.

What has to be right before the change

A new board can't go onto an installation that isn't safe to connect it to. The earthing and the main bonding to the incoming gas and water pipes have to be adequate, and so do the meter tails and the network operator's equipment at the meter.

The standard price assumes the main bonding already meets the regulations, the meter sits close to the board and the tails don't need upgrading. Anything that falls short is put right first, on a separate written quote.

An old fuse box will carry on with a small leak to earth on one circuit, and an RCD won't. That's why every existing circuit is tested before it goes onto the new board, and one with a dangerous fault stays off it until it has been repaired.

I'd rather start from a full condition report on the whole installation, so any problems are known before the day of the change.

An overheated or damaged board has to come out quickly, but the same checks apply before its replacement is connected.

On the day of the change

The whole house is off while the board is changed. If there is no isolating switch between the meter and the board, the network operator has to take out its own fuse first, so the change is booked around that. I'll check which you have.

Plan for the fridge and freezer to be off while the work is done, and for clocks and timers to need resetting afterwards.

Each circuit on the new board is labelled, so anyone can tell what every switch does, and the notice about testing the RCDs goes on the front.

When the wiring behind the board is too old

Some houses still have lighting circuits with no earth conductor, wired before earths were run to every light. A circuit like that should have an earth added or be rewired before it goes on the new board. If that isn't wanted, it can only go back on with every metal fitting and switch on it replaced by an all-insulated one, and a warning notice at the board.

Rubber-insulated or lead-sheathed cable is another matter. Moving it at the board can crack the insulation, so the industry guidance is to finish rewiring those circuits before the board is changed.

Is an old fuse box illegal?

No. There's no law that makes a homeowner bring an installation up to the current regulations, and rewireable fuses still give proper overcurrent protection.

Landlords are in a different position. A rented home in England needs a new condition report no more than 5 years after the last one, and anything coded as dangerous or potentially dangerous must be put right, which sometimes means a new board.

For everyone else, whether the board goes comes down to what the testing finds.

Part P and the certificate for a board change

In England, Part P makes the replacement of a consumer unit notifiable. Electricians on a competent person scheme can self-certify the work. Otherwise a registered third-party certifier inspects it, or a building notice goes to the local authority before the work begins.

Whichever route applies, the board is tested against the wiring regulations. The certificate for the change is an Electrical Installation Certificate, with test results for each of its circuits and a record of any defects on the circuits that stayed.