Key takeaways
- Most standby generator failures to start come from batteries, fuel and neglect, not from the engine itself.
- Run the generator regularly, and under load when you can: long periods of light-load running cause problems of their own.
- Follow the manufacturer's service intervals; the checklist here is a framework, not a replacement.
- Keep a log: it shows what was done, and spots trends before they become failures.
A standby generator has an unusual job. It may sit idle for weeks or months, then be expected to start immediately, take the load and run reliably for as long as the mains is off. When it doesn’t start, the failure usually happens at the worst possible moment.
The good news is that most generator problems are preventable. Batteries, fuel, coolant and simple neglect cause far more failures than the engine itself. A regular, recorded routine catches them early.
This checklist is a practical framework for a typical diesel standby set. Always follow the manufacturer’s manual for your specific model, including its service intervals, oils, filters and coolant types, and your site’s safety procedures.
Weekly: a quick walk-round
These take a few minutes and are often done by site staff.
- Look for leaks of fuel, oil or coolant under and around the set.
- Check fluid levels: engine oil, coolant and fuel in the day tank.
- Check the controller: it should be in automatic (if that’s how your site runs) with no alarms or warnings.
- Look at the batteries: terminals clean and tight, no swelling or leaks, charger showing normal operation.
- Check the surroundings: air intakes and exhaust clear, nothing stored against the set, the room or enclosure dry.
Monthly: run it
A generator that never runs is a generator nobody can trust. A regular test run circulates oil, charges the battery, exercises the controls and proves the set can start.
- Start and run the set as the manufacturer recommends, watching for smooth starting, normal smoke and normal noise.
- Check the readings: oil pressure, coolant temperature, voltage, frequency and battery charging, and record them.
- Run under load when you can. Diesel engines that spend long periods running at very light load can suffer from incomplete combustion and fuel and carbon build-up in the exhaust system, often called wet stacking. A periodic run with a meaningful load, using the building load or a load bank, helps avoid it. Your manufacturer’s guidance will say what load and duration suit your set.
- Test the changeover, if you have an automatic changeover panel, in a planned way so the transfer to and from generator power is proven.
Quarterly and half-yearly: closer checks
- Batteries: check voltage and, where applicable, electrolyte level; clean terminals; test or replace ageing batteries before they fail. Starting batteries are one of the most common causes of a failed start.
- Belts and hoses: look for cracks, glazing, softness and correct tension.
- Air filter: check the restriction indicator if fitted; clean or replace as required.
- Coolant: check condition and antifreeze or inhibitor strength as specified.
- Fuel system: drain water from the water separator; inspect lines and connections.
- Electrical connections: check for tightness and signs of overheating in the generator terminal box and changeover panel.
Yearly (or at the manufacturer’s interval)
- Change engine oil and filters (oil, fuel and air) at the manufacturer’s interval, which for standby sets is often time-based as well as hour-based.
- Fuel quality: diesel stored for long periods can degrade and attract water and microbial growth. Check the tank for water and sediment, and consider fuel testing or polishing for large stored volumes.
- Cooling system: inspect the radiator for blockage and clean it; check the coolant and replace it at the specified interval.
- Exhaust system: check for leaks, corrosion and secure mounting.
- Controller and protection: test alarms and shutdowns (low oil pressure, high temperature, overspeed) as the manual describes.
- Load test: run the set at a substantial load for a sustained period, to prove it can carry the site’s requirement.
Keep a log
Record every check, run and service: the date, hours, readings and anything unusual. A log does three things:
- It shows what was done and when, for audits and insurance.
- It reveals trends, such as rising coolant temperature or slower starts, before they become failures.
- It tells the next engineer the generator’s history.
Common warning signs
Call for help before the next mains failure if you notice:
- slow or hesitant starting
- black, white or blue smoke beyond a brief puff at start-up
- unusual knocking, vibration or noise
- rising coolant temperature or falling oil pressure
- fuel, oil or coolant leaks
- frequent battery or charger alarms
When a maintenance contract makes sense
If your site depends on backup power, a maintenance contract puts the generator on a planned schedule with a report after each visit and priority response if it fails. It is especially useful when the people on site are busy with other work, which, for a machine that sits quietly in a corner, is most of the time.
To discuss a generator that needs attention, or planned maintenance for your site, get in touch.
General guidance based on common engineering practice. Always follow the equipment manufacturer’s instructions and your site’s safety procedures.