Quick answer
When a commercial boiler breaks down, put safety first. If you smell gas or a CO alarm sounds, leave and call 0800 111 999. Otherwise check the controls are calling for heat, record fault codes and the system pressure, see whether other boilers are running, and call a qualified commercial heating engineer. Do not open the boiler or repeatedly reset it.
Step 1: check for danger
Gas smell or CO alarm? Do not operate switches. Leave the area, get people into fresh air and call the National Gas Emergency Service on 0800 111 999. Call 999 if anyone is unwell.
Also keep clear if there is water near electrics, steam or burning smells in the plant room.
Step 2: confirm what the building has lost
- heating, hot water or both?
- the whole building or specific zones?
- since when, and was anything changed beforehand (maintenance, power cut, holiday schedule)?
Step 3: read the controls, not the casing
From the boiler display, BMS or controller, note:
| Check | Why it matters |
|---|---|
| Fault code or lockout message | Points to ignition, flame, fan, flue, pressure or overheat faults |
| Number of boilers running | A cascade may still be carrying the load |
| System pressure gauge | Low pressure locks boilers out |
| Time schedule and setpoints | The boiler may simply not be asked to run |
| Other plant alarms | A pump or pressurisation fault may be the real cause |
Photograph the displays before anyone resets anything.
Step 4: decide whether it is urgent
Call now if the building has lost heating or hot water and people or operations are affected, if several boilers have locked out, or if there is a leak. If heating is being maintained by other boilers, the repair may be suitable for the next working day; discuss it on the call.
Step 5: call with the right information
Give the postcode, boiler make and model, number affected, fault codes, pressure reading, affected areas and plant room access. Our 24/7 contact line is 020 7998 9005.
What not to do
- do not open boiler casings or touch gas valves
- do not bypass interlocks or safety devices
- do not repeatedly reset a boiler in lockout
- do not top up or vent the system unless trained and authorised
Managing occupants while you wait
Tell occupants what is happening, consider moving people to warmer areas, and assess whether temporary heating is safe and suitable. HSE guidance suggests workplace temperatures should normally be at least 16°C.
Next steps
See emergency commercial boiler repairs and the plant room emergency checklist.
Frequently asked questions
Should I reset the boiler before calling?
Only if your site procedures and the manufacturer's instructions allow an authorised person to make a single reset. If it locks out again, leave it and call. Never reset if there is a gas smell or CO alarm.
How do I know if it is the boiler or the heating system?
If the boiler shows a fault or lockout, start with the boiler. If the boilers are running but the building is cold, the fault is more likely in circulation or controls. See commercial heating repairs.
UK guidance and references
Primary and industry sources relevant to this subject. Always check the current edition and how it applies to your building.
- Gas safety Health and Safety Executive
- Carbon monoxide poisoning NHS
- Workplace temperatures Health and Safety Executive
This guide is general information for commercial building operators. It does not replace an assessment by a competent engineer. If you smell gas or a CO alarm sounds, leave the area and call 0800 111 999; if there is a risk to life, call 999.