Quick answer
The seven main warning signs are unusual noise or vibration, water leaks, unusual smells, rising comfort complaints, repeated alarms or fault codes, an unexplained rise in energy use, and equipment short cycling. Burning smells, electrical faults and leaks near electrics need immediate attention. Most other signs should be logged and investigated within days, before they become breakdowns.
Spotting problems early
Most commercial HVAC breakdowns are preceded by warning signs. Facilities teams, building managers and occupants usually notice them first. Logging and acting on them early is cheaper and less disruptive than waiting for a failure. For what to do once something has already failed, see the HVAC breakdown guide.
The seven signs at a glance
| Sign | Likely causes | Urgency |
|---|---|---|
| 1. Noise or vibration | Worn bearings, loose or worn belts, fan imbalance, loose panels, compressor problems | Days, or immediately if severe |
| 2. Water leaks | Blocked condensate drains, failed condensate pumps, pipe or valve leaks, frozen coils | Immediately if near electrics or in critical areas |
| 3. Unusual smells | Burning (electrical), musty (standing water or dirty filters), chemical | Burning is an emergency; others within days |
| 4. Comfort complaints | Controls, sensors, valves, airflow or capacity problems | Days |
| 5. Alarms and fault codes | Equipment protecting itself from a fault | Depends on the alarm; repeated alarms need investigating |
| 6. Energy use rising | Schedules, simultaneous heating and cooling, fouled coils, failed heat recovery | Weeks |
| 7. Short cycling | Oversizing, control faults, refrigerant problems, sensor location | Days |
1. Unusual noise or vibration
New grinding, screeching, rattling or knocking sounds usually mean a mechanical problem: worn bearings, a slipping or damaged belt, an unbalanced fan or something loose. Problems like these get worse, and a bearing that is left to fail can damage the motor or fan.
2. Water leaks
Water from ceiling cassettes, fan coil units or AHUs usually comes from a blocked condensate drain or a failed condensate pump. It can also come from a leaking valve or pipe joint, or from a coil that has frozen. Water near electrical equipment or above IT equipment needs immediate attention. See fan coil unit problems.
3. Unusual smells
- Burning or electrical smell: treat as an emergency. Isolate the equipment if it is safe to do so and follow your fire procedures.
- Musty or damp smell: often standing water in drain trays, dirty filters or contaminated coils. This is a hygiene issue that needs cleaning and investigation.
- Gas smell: leave the area and call the National Gas Emergency Service on 0800 111 999.
4. Rising comfort complaints
When complaints increase, look for patterns. Is it one room, one floor or the whole building? Is it at certain times of day? Patterns help an engineer find the cause faster. See why some office rooms are too hot or too cold and commercial HVAC not cooling.
5. Alarms and fault codes
A fault code means the equipment has detected a problem and is usually protecting itself. Resetting it may restore operation for a while, but the cause is still there. Repeated trips need investigating. See why commercial HVAC keeps tripping.
6. Rising energy use
An unexplained rise in electricity or gas use, when occupancy and weather have not changed, often means equipment is running out of hours, heating and cooling are running at the same time, or heat exchangers are fouled. See our energy efficiency guide.
7. Short cycling
Short cycling means equipment switches on and off far more often than it should. It wears out compressors and contactors and gives poor comfort. Causes include control problems, a badly placed sensor, refrigerant issues and oversized plant.
What to record before you call
- Which unit, area or floor is affected
- When the problem started and whether it is getting worse
- Fault codes on controllers and alarms on the BMS
- Photos of leaks, damage or controller displays
- Anything that changed recently: fit-out works, power interruptions, controls changes
Do not open panels or work on electrical, refrigerant or rotating parts. Inside HVAC equipment there are live components, moving fans and pressurised refrigerant.
Next steps
For non-urgent issues, arrange a repair visit. If warning signs keep appearing, a planned maintenance programme will usually find them earlier. For urgent problems, use our 24/7 contact line on 020 7998 9005 or see emergency HVAC support.
Frequently asked questions
Is a noisy HVAC unit dangerous?
Usually not immediately, but grinding, screeching or knocking often means bearing, belt or fan damage that will get worse. Isolate the unit if the noise is severe or getting worse quickly, and get it inspected.
When is a smell an emergency?
A burning or electrical smell, or smoke, is an emergency: isolate the equipment if it is safe to do so and follow your fire procedures. If you smell gas, leave the area and call the National Gas Emergency Service on 0800 111 999.
What should I record before calling an engineer?
Record which unit or area is affected, when the problem started, any fault codes or BMS alarms, photos of leaks or damage, and whether anything changed recently, such as a fit-out, power cut or controls change.
UK guidance and references
Primary and industry sources relevant to this subject. Always check the current edition and how it applies to your building.
- Workplace temperatures Health and Safety Executive
- Ventilation in the workplace Health and Safety Executive
- Electricity at work Health and Safety Executive
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.