How often should planned maintenance actually happen?

"How often should we service this?" sounds like a question with a single correct answer, and vendors and manufacturers are generally happy to supply one. In practice, a manufacturer's recommended interval is a reasonable starting point, not a complete answer — it's typically calculated for average conditions, and very few real assets sit in exactly average conditions.

Manufacturer guidance is a floor, not a fixed answer

A manufacturer's service interval is usually built around typical usage and typical environment. An asset running harder than typical, in a harsher environment, or supporting a higher-criticality function than typical may reasonably need attention more often than the manual suggests. Treating the manufacturer figure as an untouchable rule, rather than a sensible default to adjust from, is one of the more common ways PPM schedules end up wrong in either direction.

Let service history adjust the interval over time

An asset's own service history is the best evidence available for whether its current interval is right. An asset that's never had an issue between visits might genuinely tolerate a longer interval; one that keeps generating faults shortly before its next scheduled check is telling you, fairly directly, that the interval is too long for its actual condition. This is a case where the record itself should feed back into the plan, not just document that the plan happened.

Criticality sets the floor, condition adjusts it

The cleanest way to think about frequency is as two separate inputs. Criticality sets a floor — a safety-critical asset doesn't get its interval stretched just because it's been reliable, because the cost of being wrong is too high. Condition and usage then adjust within whatever that floor allows, for everything that isn't safety-critical, based on genuine evidence rather than a hunch about how things seem to be going.

• –Start from manufacturer guidance, then adjust for actual usage intensity and environment
• –Never stretch the interval on a safety-critical asset based on a good run of reliability alone
• –Let a pattern of faults shortly before the next scheduled check push the interval shorter
• –Review intervals periodically as a deliberate exercise, not only when something has already gone wrong

When it's worth involving a specialist

For anything carrying a statutory inspection obligation — lifting equipment, pressure systems, fixed electrical installations — the interval isn't really a judgement call for the facilities team to make freely; it's tied to the relevant regulation and, in many cases, a competent person's own assessment of the specific asset. For everything else, adjusting frequency based on genuine condition and usage evidence is a reasonable, defensible thing for a facilities team to own directly, built on top of a PPM schedule that's actually being followed in the first place.

Letting the record argue with the interval

An air handling unit serviced quarterly, where the last eight visits recorded nothing beyond filter changes and a clean bill, is telling you something. So is one on an annual interval that has generated three unplanned call-outs in eighteen months. In both cases the service history is making a case the schedule has not heard, because the interval was set at commissioning and nothing since has prompted a review.

Adjusting intervals on evidence is legitimate for discretionary maintenance and emphatically not for anything with a statutory or insurer-mandated frequency, where the interval is not yours to move. Keeping those two categories visibly separate in the schedule is what makes it safe to be flexible with one of them.

Common mistakes

• –Treating manufacturer guidance as a fixed requirement rather than a starting point
• –Adjusting an interval that is actually set by statute, an insurer or a written scheme
• –Changing frequency on one engineer's opinion without reference to the service record
• –Never reviewing intervals after commissioning, however the asset behaves
• –Extending an interval to relieve workload rather than because the evidence supports it
• –No record of why an interval was set, so the next person cannot judge whether to change it

For anything with a statutory inspection obligation specifically, always confirm the current required interval against the relevant regulation or ACOP and a competent assessor's own recommendation, rather than treating anything in this piece as the final word.