Fire Alarm Not Working

Your mains-wired fire alarm system is showing a fault or not responding to tests.

£80 – £300High Risk

What is this?

Mains-wired fire alarm systems are found in many UK homes, particularly those built or renovated after 1992 when Building Regulations began requiring them. A fire alarm that is not working leaves you without early warning of fire, which is a serious safety issue. These systems are different from standalone battery smoke alarms.

Common causes

Mains supply interrupted to the alarm circuit
Backup battery dead in one or more detectors
Detector head contaminated with dust or insects
Wiring fault on the interconnected alarm circuit
Detector has reached end of life (typically 10 years)
Base unit fault preventing the detector from seating correctly

Is it dangerous?

A non-working fire alarm is a serious safety risk. Fire alarms save lives by providing early warning, giving you critical time to evacuate. If your mains-wired alarm is not working, fit temporary standalone battery smoke alarms immediately while you arrange a repair.

Can I fix it myself?

Test each alarm using the test button. If one does not respond, check it is properly seated in its base. Try removing it, blowing out any dust, and refitting. Check the consumer unit for a tripped MCB on the alarm circuit. Replace the backup battery in any alarm showing a battery fault. Check the age of your alarms — they should be replaced every 10 years.

When to call an electrician

Call an electrician urgently if none of your mains alarms are working, if the alarm circuit keeps tripping, if alarms need replacing due to age, or if you need additional alarms fitted to comply with Building Regulations. Do not leave your home without working fire alarms.

What will an electrician do?

Test the mains supply to the alarm circuit

Test each detector and its interconnection

Replace detector heads that have reached end of life

Check and repair wiring faults on the alarm circuit

Install additional detectors where required by regulations

Issue a test certificate confirming the system is working

Typical cost

£80 – £300

Replacing detector heads is the most common job. Adding new detectors to an existing circuit costs more. A complete new mains-wired system for a 3-bed house typically costs £200-£400.

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Sources & References

Frequently Asked Questions

How do I know if my fire alarms are mains-wired?

Mains-wired alarms are typically screwed to a ceiling base plate and do not have a removable battery compartment on the front. They are interconnected — when one triggers, they all sound.

How often should mains fire alarms be replaced?

All smoke and heat detectors should be replaced every 10 years, even if they appear to work. The sensor degrades over time and becomes less effective at detecting smoke or heat.

What alarms do I need in my home?

Under current Building Regulations, you need smoke alarms on every floor of your home, a heat alarm in the kitchen, and they should be interconnected. Rental properties in England have additional requirements under the Smoke and Carbon Monoxide Alarm Regulations.

Can I replace mains-wired alarms myself?

Replacing a detector head on an existing base is straightforward. However, any changes to the alarm circuit wiring should be done by a qualified electrician and may need to comply with Part P of the Building Regulations.

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