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Preventive vs corrective maintenance
Preventive maintenance is done on a schedule to stop a failure. Corrective maintenance responds to one that already happened. That part is easy. The hard part is that every department is told to shift the ratio between them, almost nobody is told what the right ratio is, and the honest answer is that nobody knows yours.
- Biomedical engineering
- Hospital operations
- Clinical engineering
What is the difference between preventive and corrective maintenance?
Definition
Preventive and corrective maintenance
Preventive maintenance is planned work performed on a schedule to reduce the chance of a failure. Corrective maintenance is unplanned work performed because a failure has already occurred. The first is chosen; the second is imposed.
The words people also use: preventive is called planned, scheduled or PPM; corrective is called reactive, breakdown or run-to-failure. They mean the same things, and the multiplicity of names is a reasonable clue that the category boundary is fuzzier than it looks.
The genuinely interesting property is not the definition, it is the asymmetry in how each one competes for attention. A corrective job has somebody asking about it. A preventive job has a date.
How they differ, beyond the obvious
The definitions are easy. The differences that matter are about cost, visibility and who is asking.
| Aspect | Preventive | Corrective |
|---|---|---|
| Trigger | A schedule you set | A failure that happened |
| Who is asking about it | Usually nobody | A ward, loudly, now |
| Cost when it happens | Known and budgeted | Unknown until it is over |
| Cost when it does not happen | Nothing visible | Not applicable |
| Downtime | Planned, negotiable, short | Unplanned, includes waiting for parts |
| Evidence produced | A record that it was done | A record that it broke |
| Failure mode of the process | Quietly deferred until it is a paper programme | Absorbed as normal until nobody questions it |
| What it competes with | Clinical use of the device, and loses | Nothing. It is already broken |
Preventive and corrective work compared on what actually distinguishes them
Why the preventive-to-corrective ratio is the wrong target
Because it is a number you can move by doing more useless preventive work, and every department under pressure eventually discovers that.
The ratio is quoted constantly and gamed easily. If the target is a higher proportion of preventive work, the fastest route is to schedule more of it: add low-value checks to easy devices, and the percentage climbs without a single failure being prevented. The metric improves, the estate does not, and nobody has done anything dishonest.
The deeper problem is that there is no correct ratio and anybody quoting one is quoting somebody else's estate. It depends on your equipment, its age, its duty cycle, the manufacturer guidance and your risk appetite. An estate of new, reliable, low-consequence devices might rationally do very little preventive work. An estate of ageing, critical, hard-to-source ones might rationally do a great deal. The same ratio would be a failure in one and a triumph in the other.
What is worth measuring instead is narrower and harder to game: whether the preventive work you decided to do actually happened, and whether the failures you are getting are the kind preventive work would have caught. The second question is the one that tells you your intervals are wrong, and almost nobody asks it.
What to measure instead
Four questions that resist gaming, all answerable from your own records.
Did the preventive work you planned actually happen?
Not the ratio, the completion. A programme with excellent coverage on paper and forty per cent completion is a programme that is not running, and the ratio will not tell you that.
Were the failures preventable ones?
A corrective job on a device that was overdue is information about your programme. A corrective job on a device that was up to date is information about your interval. Most estates never separate these two, and they mean opposite things.
How much of the corrective time was waiting?
Waiting for a part, an engineer, or ward access. That fraction is a supply problem wearing a maintenance costume, and preventive work will not fix it.
What did the deferrals cost?
Every preventive job deferred is a decision. If the deferred ones and the failures never get compared, the department is arguing for its programme from belief rather than from its own evidence.
Why preventive work loses, and what actually helps
Because its value is invisible when it succeeds, so it loses every contest with work whose absence is visible. Only escalation changes that.
A broken pump on a ward is loud, specific and has a person asking about it. A pump due a check is quiet, and skipping it produces no consequence today, this week or probably this quarter. Every individual deferral is defensible and the aggregate is a programme that exists on paper. This is not indiscipline; it is incentives working exactly as you would predict.
Software does not solve that and anyone claiming otherwise is selling. What it can do is stop the deferral being invisible: an overdue task that escalates to somebody accountable while it still matters converts a drift into a decision. The decision may still be to defer, which is legitimate. What kills programmes is deferral nobody chose.
The other thing that helps is unglamorous and rarely done: reviewing intervals against a year of your own failure history. Intervals set on manufacturer guidance and a guess in year one can be set on guidance and evidence in year two, and almost no estate does this, which is why most intervals are whatever somebody typed at the start.
What Rydya will not tell you here
It will not tell you your ratio should be any particular number, and it ships no intervals. How often a device needs attention depends on the manufacturer, the model, its duty cycle and your risk appetite, and a default would be software making a clinical claim about equipment it has never seen. What it does is hold the interval you set, generate the work far enough ahead that it can be arranged, escalate slippage to a named person while it still matters, and record what happened so you can review the interval against evidence rather than memory.
Questions
What is the difference between preventive and corrective maintenance?
Preventive maintenance is planned work done on a schedule to reduce the chance of a failure. Corrective maintenance is unplanned work done because a failure already happened. The first is chosen, the second is imposed. The difference that actually matters is that a corrective job has somebody asking about it and a preventive job only has a date.
What is a good ratio of preventive to corrective maintenance?
There is no correct ratio, and anyone quoting one is quoting somebody else's estate. It depends on your equipment, its age, duty cycle, manufacturer guidance and risk appetite. The ratio is also easily gamed: schedule more low-value checks on easy devices and it climbs without preventing a single failure. Measure completion and whether your failures were preventable instead.
Why does preventive maintenance always get deferred?
Because its value is invisible when it succeeds. A broken pump is loud and has someone asking; a pump due a check is quiet, and skipping it produces no consequence this quarter. Every deferral is individually defensible and the aggregate is a paper programme. That is incentives working as predicted rather than indiscipline, and no amount of policy fixes it.
How do we know if our intervals are right?
Separate your corrective jobs into two piles: devices that were overdue, and devices that were up to date. The first tells you about your programme, the second about your interval. Most estates never separate them, which is why most intervals are still whatever somebody typed in year one, despite a year of real failure history now being available.
See it on your equipment
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