Quick answer
A commercial HVAC system that keeps tripping usually has an electrical, mechanical, refrigerant or control fault. Common causes include failing motors or compressors, short circuits, water reaching electrics, high-pressure trips from dirty condensers, low-flow trips on chillers and faulty sensors. Repeated resets can cause serious damage, so record the fault code and call an engineer.
Two kinds of “tripping”
“Tripping” can mean two different things, and it helps to know which you have:
- Electrical protection trips: a circuit breaker, RCD or fuse disconnects the supply. The unit goes completely dead.
- Equipment safety trips: the unit’s own safety controls stop it, usually showing a fault code or alarm. Power is still present.
Electrical causes
| Cause | Typical sign |
|---|---|
| Failing compressor or fan motor | Trips on start-up; may hum or run hot |
| Water in electrical components | Trips after rain or when condensate overflows |
| Damaged cables or loose terminals | Intermittent trips, burning smell, discolouration |
| Failing capacitor or contactor | Motor struggles to start, then trips |
| Overloaded circuit | Trips when other equipment runs at the same time |
Electrical faults can cause fires. If you notice burning smells, smoke, scorching or crackling, isolate the equipment if safe to do so and call an engineer. In an emergency call 999.
Refrigerant and pressure trips
- High-pressure trips: the system cannot reject heat. Typical causes are dirty condenser coils, failed condenser fans or obstructed outdoor units. Common on hot days.
- Low-pressure trips: often low refrigerant charge from a leak, a blocked expansion device or a frozen indoor coil from poor airflow.
Flow and airflow trips
Chillers and heat pumps have flow switches that stop the compressor if water flow is too low, for example from a failed pump, closed valve, blocked strainer or air in the system. Air handling units may stop on fan failure, filter alarms or frost protection.
Controls and sensor faults
A faulty temperature or pressure sensor can trip healthy equipment. Loose wiring, damaged sensors and incorrect settings after changes to the BMS are common culprits.
What to do
- Note the fault code, alarm text and time it happened.
- Check for obvious hazards: water, smoke, damage.
- Allow at most one reset if it is safe and permitted on site.
- If it trips again, leave the unit off and protect affected areas.
- Call an engineer with the details.
For urgent cases call 020 7998 9005. Otherwise see HVAC repairs and, for central plant, chiller services.
Frequently asked questions
Is it safe to reset a tripped HVAC breaker?
One reset after checking for signs of water, burning smells or damage is reasonable. If it trips again, leave it off. Repeated resets on a faulty circuit or compressor can cause damage or create a fire risk.
What is a high-pressure trip?
A safety device that stops the compressor when refrigerant pressure gets too high, usually because the system cannot reject heat. Dirty condensers, failed condenser fans, blocked airflow round outdoor units or overcharging are common causes.
UK guidance and references
Primary and industry sources relevant to this subject. Always check the current edition and how it applies to your building.
- Electrical safety at work Health and Safety Executive
- F gas in refrigeration and air conditioning GOV.UK
This guide is general information for commercial building operators. It does not replace an assessment of your building by a competent engineer. If there is an immediate risk to people, contact the emergency services first.