AFDDs in HMOs London — 15 October 2026 Deadline & Costs

AFDDs in London HMOs: what the 15 October 2026 deadline actually means

Short answer: BS 7671 Amendment 4 makes arc fault detection devices (AFDDs) mandatory on socket-outlet final circuits rated up to 32 A in HMOs, purpose-built student accommodation, care homes and other higher-risk residential buildings. It is not retrospective — nobody has to rip out a working consumer unit on 15 October 2026. It applies to new installations and alterations designed after the old standard is withdrawn. If you are replacing a board in an HMO after that date, it needs AFDDs.

What Amendment 4 changed

BS 7671:2018+A4:2026 was published on 15 April 2026. The previous version — BS 7671:2018+A2:2022+A3:2024 — is formally withdrawn on 15 October 2026. From that point, new installation design work is expected to be to Amendment 4.

The relevant change is a redraft of Regulation 421.1.7. Under Amendment 4, AFDD protection moves from “recommended” to required on final circuits supplying socket outlets with a rated current not exceeding 32 A, in:

• houses in multiple occupation (HMOs)
• purpose-built student accommodation
• care homes
• other higher-risk residential buildings

For an ordinary single-family home that does not fall into one of those categories, AFDDs remain a recommendation, not a requirement. That distinction matters, because a lot of the advice circulating at the moment blurs the two.

We covered the wider set of changes in our guide to BS 7671 Amendment 4 for London homeowners and businesses.

Does every London HMO need AFDDs on 15 October 2026?

No — and this is the single most misunderstood point.

BS 7671 is not retrospective. An existing installation that was compliant when it was designed and installed does not become illegal because a new amendment has been published. What changes is the standard that new work is designed to.

In practice, the requirement bites when one of these happens after the withdrawal date:

• You replace the consumer unit. A new board serving socket circuits in an HMO should be specified with AFDDs.
• You add or alter a socket circuit — a new ring, a kitchen refit, a converted room.
• You rewire, in full or in part.
• You convert a property into an HMO, or add units to an existing one.

If none of those apply and your board is sound, you are not obliged to do anything on 15 October. If you were already planning a board change, though, timing it deliberately is worth a conversation — see the cost section below.

What AFDDs cost in a London HMO

An AFDD detects the electrical signature of an arcing fault — a loose terminal, a nailed-through cable, a damaged flex — and disconnects before it can ignite surrounding material. That is why the regulations single out buildings where people sleep and cannot easily self-evacuate.

They are considerably more expensive than the RCBOs they sit alongside. Indicative materials costs, which we quote separately from labour:

A typical HMO board has two to four socket-outlet final circuits. Fitting AFDDs to those circuits instead of plain RCBOs therefore tends to add roughly £150 – £400 in materials to a board change. Only the socket circuits up to 32 A need them — lighting, showers and cookers do not, so you are not paying to populate the whole board.

Our labour for a consumer unit replacement starts at £450, and every price we quote is labour-only — the board and the devices are quoted separately so you can see exactly what the parts cost. Our minimum charge is £108 (£90 + VAT). There is a fuller breakdown on our fuse board replacement cost page.

The timing point: if a board in one of your HMOs is close to needing replacement anyway, doing it before the switchover is cheaper in materials. Doing it after buys you a board that is specified to the current standard and will not need revisiting. Neither is wrong — it depends on how long you intend to hold the property.

How this affects your EICR

An EICR assesses an installation against the current edition of BS 7671, but departures on older installations are coded on the inspector’s judgement of actual risk, not automatically failed.

The absence of AFDDs on an existing HMO socket circuit is normally recorded as a C3 — improvement recommended. A C3 does not make the report unsatisfactory and does not, on its own, put you in breach of the Electrical Safety Standards in the Private Rented Sector Regulations. What produces an unsatisfactory report is a C1 or C2, and those are about danger present or potentially dangerous conditions.

Be sceptical of anyone telling you a missing AFDD is a C2 and quoting you for an emergency board change. If you want a second opinion on a report, we are happy to look at it. Our HMO EICR page explains how the inspection works, and HMO electrical compliance covers the fire alarm, emergency lighting and PAT obligations that sit alongside it.

Nuisance tripping — the honest caveat

Early AFDDs had a reputation for tripping on things that were not faults: brushed motors, some cheap LED drivers, certain vacuum cleaners. Current-generation devices are considerably better, but in an HMO — where you have no control over what tenants plug in — it is still worth specifying a reputable manufacturer and matching the AFDDs to the board rather than mixing brands.

It is also a good argument for doing the board change properly rather than cheaply. A poorly terminated installation will give you arcing signatures and therefore trips, which is precisely the outcome landlords fear.

What to do before 15 October 2026

1. Work out which of your properties are actually HMOs under the definition your borough uses. London boroughs vary on additional and selective licensing.
2. Check the age and condition of each consumer unit. A plastic board, or one with no RCD protection, is due for replacement on its own merits — the AFDD question just affects the specification.
3. Check when each EICR expires. HMOs need one every five years, and a lot of London stock was tested in the 2020–2021 wave, so renewals are landing now.
4. Get board changes specified, not just priced. A quote that does not say what devices are going in is not comparable to one that does.
5. Do not panic-buy. Nothing in Amendment 4 requires you to retrofit AFDDs into a compliant existing installation.

Common questions

Are AFDDs required in a normal rented flat? Not as a requirement. A single-household rented flat is not an HMO, so AFDDs remain recommended rather than mandatory on its socket circuits.

Do I need AFDDs on lighting circuits? No. The requirement is specific to socket-outlet final circuits rated up to 32 A.

Can AFDDs be added to my existing board? Sometimes, if the board accepts them and there is space on the busbar. Often it is more sensible to plan it into a board replacement. We will tell you which applies once we have seen it.

Will this affect my licence application? Councils ask for a satisfactory EICR, not for AFDDs specifically. Compliance with the current wiring regulations for any new work is expected either way.

Talk to a NICEIC-approved electrician about your HMO

We work across London on HMO boards, EICRs and licensing paperwork. Tell us how many units, how many socket circuits and what board is in there now, and we will give you a fixed labour price with the materials itemised separately — before any work starts.

Call or text 07407 627542 · alternative line 07500 721453 · email info@faelectrical.co.uk

NICEIC-approved and fully insured. Minimum charge £108 (£90 + VAT). All quoted prices are labour-only.

Related: BS 7671 Amendment 4 · HMO EICR London · HMO electrical compliance · Landlord EICR · All areas we cover.