Every smoke alarm has a finite life. Manufacturers stamp a date on the head and BS 5839-6:2019 confirms the ten-year service ceiling — at that point the sensor sensitivity has drifted and the unit must be replaced. The first sign is usually the end-of-life chirp: a single beep every 30-60 seconds that does not stop with a battery change because the battery is sealed for the head life.
Replacement is straightforward when the existing wiring is sound. We remove the old head from its base, verify the base wiring is BS 5839-6 compliant, fit the new head, re-pair the interlink (radio or wired) and run a full commissioning test. The whole point takes about 20 minutes. The replacement is £180 per point — the same rate as a fresh install, because the work content is broadly the same.
Sometimes replacement is the wrong answer. If the existing system is partial coverage (LD3 escape route only, in a property that should be LD2), or if the old heads are mixed-brand or non-interlinked, the right move is a full re-spec rather than like-for-like. Electrician London surveys before replacement and tells you honestly which path saves you money and which leaves you exposed at the next audit.
Why Electrician London
Like-for-like swap on existing wiring
Old head off, new head on, interconnect re-paired, commissioning re-run. Twenty minutes per point, no chasing, no making good.
End-of-life chirp resolved
The seven-second chirp every minute? End-of-life. We replace the head and reset the alarm — chirp gone, certificate fresh, ten more years of protection.
BS 5839-6 re-commissioning
Replacement is treated as a fresh commissioning event. Full test under load, interlink verification, certificate issued same day.
Re-spec advice when needed
If the existing schedule no longer meets LD2 we say so. Honest upgrade quote when it makes more sense than swapping outdated heads.
Smoke alarm replacement pricing
Per-point pricing on existing wiring. Discovery survey free with replacement booking.
Smoke alarm replacement (on existing base)
Like-for-like Grade D swap
£180 / point
Heat alarm replacement
Kitchen / plant room end-of-life
£170 / point
CO alarm replacement
Where fixed combustion appliance present
£140 / point
Full system re-spec (3-4 alarms)
When like-for-like is the wrong answer
£550
Annual inspection (post-replacement)
Engineer test, logbook entry
£85
What's included in the replacement
- Discovery survey of existing system
- Removal and safe disposal of old heads
- New Grade D alarm head (Aico, FireAngel or Kidde)
- Interconnect re-pairing (wired or radio)
- Full commissioning test under load
- BS 5839-6 re-commissioning certificate
- Minor Works certificate where wiring touched
- Logbook update and install photographs
Frequently asked questions
Why do smoke alarms need replacing at ten years?
The optical chamber accumulates dust and the sensor sensitivity drifts beyond BS 5839-6 tolerance. Manufacturer testing supports a ten-year service life and BS 5839-6:2019 codifies it. Beyond ten years the alarm may still appear to work but cannot be relied on to detect smoke at the standard set-point.
What is the end-of-life chirp?
A single chirp every 30-60 seconds, often increasing to two chirps in the final months. The chirp will not stop with a battery change because the battery is sealed for the head life. The only fix is replacement. Aico heads also display an end-of-life LED pattern.
Can I replace the head without rewiring?
Almost always yes — the bases are standardised within each manufacturer family and are designed to outlast multiple head replacements. We verify the base wiring is BS 5839-6 compliant during the survey and only replace bases if they are damaged or non-compliant. Replacement bases cost a small extra.
Does replacement need a re-certificate?
Yes — BS 5839-6 treats a head replacement as a fresh commissioning event because the new head is the device under test. We run a full commissioning test (smoke, interlink, battery) and issue a fresh certificate. Landlords use this certificate for the next licensing audit.
Can I mix old and new alarms in the same system?
Yes within the same brand family. Aico Ei3000-series heads interoperate freely; FireAngel Pro likewise. Cross-brand mixing on a radio link is not supported. Wired interconnect (3-core+E) is more forgiving but we still recommend single-brand systems.
When does replacement become a re-spec?
When the existing schedule no longer meets BS 5839-6 LD2 — for example, an old LD3 system in a property that has become a licensed HMO. In that case we quote a full re-spec rather than replacing heads on an outdated schedule. Re-spec for a 3-4 alarm interlinked system runs £550.
How long does the chirp take to stop after replacement?
Immediately. The chirp is generated by the old head and stops the moment that head is taken off the base. The new head powers up silent and runs a self-test on its first sixty seconds, then enters quiescent state.
Do I get the same warranty as a new install?
Yes — every replaced head carries the full manufacturer warranty (usually ten years on Aico, FireAngel and Kidde) plus our workmanship guarantee on the install. The new BS 5839-6 commissioning certificate resets the audit clock.
Related services
NICEIC engineers, same-day across London.
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Call 020 3633 5557