Preventive vs. Reactive Maintenance: Which Strategy Belongs Where?
Software vendors like to say preventive maintenance always beats reactive maintenance. Most experienced maintenance supervisors know it depends on the asset. Preventive maintenance pays off well on equipment that is critical, expensive, or hard to replace. On assets where fixing things after they break is cheaper, a PM schedule mostly uses up labor.
A maintenance program shouldn't aim for the highest possible PM count. Its job is to spread a limited amount of labor and parts money across hundreds of assets so that total cost and risk stay as low as possible. The framework below is the one most public works, utility, and facility teams end up using after their first few years with a CMMS.
The three strategies
- Reactive maintenance (run-to-failure). You fix the asset when it breaks. Each repair is cheap on its own, but it becomes the most expensive approach when a failure has serious consequences.
- Preventive maintenance (PM). Work is scheduled at a fixed interval, based on time, meter readings, or cycles, to head off failures. On critical assets it is inexpensive insurance.
- Predictive maintenance (PdM). Work is triggered by the asset's condition. Sensors, vibration readings, oil analysis, or telemetry open a work order only when a reading crosses a threshold. It is the most efficient option when you have the data, and more than you need when you don't.
The decision matrix
Rate each asset on two things:
- Consequence of failure. If this asset goes down without warning, what does it cost in money, service disruption, and public trust?
- Cost of prevention. What does the PM cycle cost in labor, parts, and downtime?
Those two ratings point to a strategy:
- High consequence, low prevention cost: frequent PM. If Lift Station 3 goes down on a holiday weekend, that single event will cost more than a year of quarterly inspections.
- High consequence, high prevention cost: predictive maintenance. Use sensors, telemetry, and runtime data to schedule work only when it is needed. The data investment pays for itself on these assets.
- Low consequence, low prevention cost: light PM. An annual inspection is usually enough.
- Low consequence, high prevention cost: reactive. Run it until it fails. The light fixture in a storage room doesn't need a quarterly inspection.
A useful test: compare the cost of one unplanned failure with the cost of a year of preventive checks. If the failure costs more, schedule PM. If it costs less, reactive repair is usually the cheaper choice.
Where municipalities most often get it wrong
We see two common problems.
PM on paper only. All assets get the same quarterly check because that is what the spreadsheet calls for. Crews click "complete" without inspecting anything in depth. The completion rate looks good, and the infrastructure keeps failing.
No PM at all. The crew works hard and stays behind. Overtime eats the budget. Capital replacements arrive in waves because no one is watching assets until they fail.
Both problems have the same fix: an accurate asset registry, with PM strategies set for each asset class instead of one schedule for the whole organization.
How a CMMS supports the mix
A CMMS should let a supervisor assign a different strategy to each asset class without writing code. At minimum, it needs:
- Time-based PM. Intervals such as 30, 90, 180, or 365 days, with work orders generated automatically.
- Meter-based PM. Intervals such as 5,000 hours, 10,000 miles, or 250 cycles.
- Condition-based triggers. A work order opens when a sensor reading crosses a set threshold.
- Asset class templates. Define the PM once for "lift station," apply it to all 18 lift stations, and adjust individual assets where needed.
- PM compliance reporting. A report by division showing what was scheduled, completed, and missed. Auditors ask for this one.
Building a starter PM program
If you are starting from nothing, don't try to put all your assets on PM in the first week. Work in stages:
- List your top 20 assets by replacement cost or by consequence of failure.
- Set a starting PM schedule for each one based on the manufacturer's recommendation.
- Run that program for a quarter. Track completion and failures.
- Add the next 20 assets, and adjust intervals based on what you learned in the first quarter.
After a year, you will have a PM program you can defend that covers about 80% of your asset value weighted by consequence, and your crews won't be spending time on PMs that don't matter.
Where AI fits
AI is starting to help with tuning PM intervals. By comparing completed work order history, parts usage, and downtime, an AI assistant can flag assets where the current interval looks too frequent (no defects found in 12 cycles) or too infrequent (failures happening before the next scheduled PM). The supervisor makes the decision, and the AI points out which assets to look at. More on AI in operations.
WorkmanIQ includes time-based, meter-based, and condition-based PM, with AI suggestions for tuning intervals. See how it works