Ask ten facility managers how often their generator gets serviced and you'll hear ten different answers, "quarterly, I think," "when the vendor comes out," "it's on a contract." Ask what the standard actually requires and the room gets quiet.
Here's the full calendar, straight from the NFPA 110 framework that Texas fire codes and healthcare accreditors enforce, organized the way you'd actually run it. Print it, tape it in the generator room, and compare it against what your current vendor delivers.
Weekly: the 15-minute inspection
A documented walkaround of the Emergency Power Supply System:
- Fuel level (main tank and day tank), no visible leaks, fuel, oil, or coolant
- Battery charger operating; battery terminals clean and tight
- Block heater running (a cold diesel is a slow-starting diesel)
- Coolant and oil levels in range
- Louvers/air path unobstructed; no rodent nests, no storage piled against the unit
- Control panel in AUTO, not OFF, not MANUAL (more failed pickups trace to a switch left in the wrong position after service than to any mechanical failure)
- Alarms clear
No tools required. But it must be written down, dated, and initialed. A pencil-whipped log is the first thing an experienced inspector spots.
Monthly: run it under load, and transfer it
Two separate obligations, both monthly:
1. Exercise the generator: 30 minutes minimum, under load. For diesel units, loading should reach at least 30% of nameplate kW (or the manufacturer's recommended exhaust gas temperature). Record load readings, voltage, frequency, and temperatures during the run. An unloaded idle "test" isn't just non-compliant, it actively damages diesel engines over time (wet stacking).
2. Operate every automatic transfer switch. The ATS is the component that actually moves your building onto generator power, and it fails more quietly than the engine. Monthly operation under load, logged per switch.
Healthcare note: hospitals and similar facilities effectively test 12 times per year with 20 to 40 days between tests: the interval itself is regulated, not just the count. Two tests jammed at the end of back-to-back months can fail a survey on spacing alone.
Annually: the deep service and (usually) the load bank
- Full preventive maintenance service: oil and filter change, fuel filters, air filter, coolant condition and additives, belts and hoses, complete battery load test, control and safety-shutdown verification per manufacturer specs
- Fuel quality testing for stored diesel: stored fuel degrades and grows microbial contamination, especially in Texas heat and humidity. Annual lab testing plus polishing or treatment as indicated. Bad fuel is one of the most common causes of real-outage generator failure
- Annual load bank test: required for any diesel unit whose monthly runs don't reach the 30% threshold, which is most of them. Roughly 1.5 continuous hours at escalating load, fully documented. Full load bank guide here
Every 36 months: the endurance proof (Level 1 systems)
Systems where failure threatens life safety must pass an extended test at least once every 36 months: a minimum of 4 continuous hours under load. This is the closest thing to a real-outage rehearsal the standard requires, and the test that catches cooling-system and fuel-delivery problems a 30-minute run never will.
The record book that ties it together
Every item above generates a record: dated logs, load readings, ATS transfer entries, service invoices, fuel lab results, load bank reports, and closed-out deficiency items. Keep them in one place, in chronological order. When an inspector, surveyor, or insurance adjuster asks, compliance is whatever your records can prove.
What "on a contract" should actually mean
Measure any generator PM contract: ours included, against this schedule. The questions that separate real programs from oil-change subscriptions:
- Who performs and documents the weekly inspections: your staff or the vendor, and does the contract include training and log templates if it's your staff?
- Are monthly tests run under load with recorded readings, or is someone starting the engine and leaving?
- Is the annual load bank included or a surprise add-on invoice?
- Is fuel testing in scope?
- Do you receive an audit-ready documentation package, or do records live in the vendor's system where you can't produce them on demand?
- When a test finds a deficiency, is there a defined path from finding → quote → repair → closure, with paperwork?
Buffalo Power Solutions maintenance agreements are built directly on this calendar, testing, load banking, fuel management, and the full documentation package, for all makes and models. If your current program can't check every box above, that's a conversation worth 15 minutes.
Get the schedule off this page and onto a contract. Call (979) 985-2632 for a PM program quote, we'll review your current logs at no charge and show you exactly where the gaps are.
FAQ
How often should a commercial generator be serviced?
Weekly documented inspections, a monthly 30-minute test under load plus transfer switch operation, a comprehensive annual service (typically including a load bank test and fuel testing), and for life-safety systems a 4-hour endurance test at least every 36 months.
Is running the generator with no load a valid monthly test?
No. NFPA 110 monthly exercising requires operation under load, at least 30% of nameplate rating for diesel units. Unloaded running also promotes wet stacking in diesel engines.
Do I need quarterly maintenance visits?
The NFPA framework is weekly/monthly/annual/36-month. Many programs package the monthly and annual obligations into scheduled vendor visits, commonly four per year, with facility staff handling documented weekly checks. What matters to an inspector is that every required task and record exists, not the visit count.
What records do inspectors ask for?
Weekly inspection logs, monthly test logs with load readings, ATS operation records, annual service and load bank reports, fuel test results, and evidence that deficiencies were repaired.
A note on accuracy: Code requirements vary by jurisdiction, code edition, and facility type. NFPA standards are updated on multi-year cycles, and each Texas city adopts and amends codes on its own schedule, your local Authority Having Jurisdiction (AHJ) always has the final word. Manufacturer requirements for your specific equipment also apply. This article is general educational guidance, not engineering or legal advice. Confirm the requirements for your specific facility with your AHJ and a qualified power systems professional. Buffalo Power Solutions is happy to be part of that conversation.