Quick answer
Most commercial buildings need a mix. Preventative maintenance suits critical and statutory items such as chillers, AHUs and refrigerant systems, where failure is disruptive or leak checks are required. Reactive, run-to-failure maintenance can be acceptable for low-cost, non-critical items. Condition-based maintenance, using readings and BMS trends, sits between the two and targets effort where it is needed.
Three approaches
| Approach | How it works | Best suited to |
|---|---|---|
| Preventative (planned) | Tasks at set intervals, for example quarterly filter changes and annual coil cleaning | Critical plant, statutory items, equipment with predictable wear |
| Reactive (run to failure) | Fix things when they break | Low-cost, non-critical items with easy access and short lead times |
| Condition-based | Act on measured condition and trends | Larger plant with good monitoring, such as chillers, AHUs and pumps |
None of these is right for every asset. The best maintenance strategies combine them on purpose.
The case for preventative maintenance
Preventative maintenance keeps equipment clean, adjusted and checked, so faults are caught before they cause breakdowns. In commercial HVAC it also covers statutory duties: refrigerant systems above the F-gas thresholds must be leak checked at set intervals whatever their condition. See F-gas leak checks.
Benefits include:
- fewer unplanned breakdowns in occupied hours
- longer equipment life
- lower energy use from clean coils and filters and correct controls
- records that support compliance, insurance and asset planning
The risk is over-maintenance: doing tasks more often than needed because a schedule says so. Using a recognised task library such as SFG20, and adjusting frequencies by asset criticality, avoids this.
The hidden costs of reactive maintenance
Reactive maintenance looks cheap because there are no planned visits. The costs arrive later:
- emergency and out-of-hours call-out rates
- secondary damage, such as water leaks from blocked drains or frozen coils
- lost productivity and complaints while systems are down
- shorter equipment life and earlier replacement
- higher running costs from equipment that runs inefficiently for months before it fails
Run-to-failure can be the right choice for some items, such as a small extract fan in a store room. It is rarely right for chillers, AHUs, VRF systems or anything serving critical spaces.
Condition-based maintenance
Condition-based maintenance uses readings and trends to decide when work is needed. Examples include:
- changing filters on measured pressure drop rather than the calendar
- monitoring chiller approach temperatures to plan tube or coil cleaning
- using vibration readings to plan bearing replacement
- reviewing BMS alarms and trends to find faults before occupants notice
It needs reliable data and someone who reviews it. In practice it is usually layered on top of a planned programme, not used instead of one. See chiller monitoring.
Choosing the mix for your building
- Build an asset register listing every HVAC asset, its location, age, condition and what it serves.
- Rate criticality. What happens if this asset fails? Does it serve a server room, kitchen or occupied office floor?
- Identify statutory requirements, such as F-gas leak checks, TM44 inspections and legionella controls.
- Assign an approach to each asset: planned, condition-based or run to failure.
- Set frequencies from a recognised schedule, adjusted for duty and condition.
- Review annually using breakdown history and service reports.
A system assessment is a practical way to do steps 1 to 3 if your records are incomplete.
What this means for your budget
A balanced strategy moves spending from unplanned emergency work to planned, predictable visits, and from replacing failed equipment to extending its life. It also gives you the condition data to plan capital replacement rather than reacting to failures.
To discuss a planned approach for your building, see commercial HVAC maintenance and maintenance contracts, or call 020 7998 9005.
Frequently asked questions
Is reactive maintenance always cheaper?
It can look cheaper in the budget because there are no scheduled visits, but costs tend to arrive as emergency call-outs, secondary damage such as water leaks, shorter equipment life and higher energy use. For critical plant, those costs usually outweigh the savings.
What is condition-based maintenance?
Condition-based maintenance means acting on measured condition, such as filter pressure drop, vibration, refrigerant pressures or BMS trends, rather than only on fixed dates. It needs good data and someone reviewing it.
How do we decide which approach each asset needs?
Rate each asset for criticality, statutory requirements, cost of failure and condition. Critical and statutory assets get planned maintenance; low-risk items may be run to failure; the rest can be adjusted using condition data.
UK guidance and references
Primary and industry sources relevant to this subject. Always check the current edition and how it applies to your building.
- SFG20 maintenance standard BESA / SFG20
- Checking F gas equipment for leaks GOV.UK
- Workplace temperatures 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.