The phone pattern after a big January outage is reliable. Someone whose generator started fine in October calls to say the unit cranked, the unit clicked, the unit ran for ten seconds and quit, or the unit did nothing at all. The five failure modes below cover almost every January no-start call we get, in roughly the order of frequency. If your generator is sitting cold under three feet of snow right now, this is what is probably wrong - and what should have been caught at the fall service that did not happen.
Failure one: the battery is dead
The single most common winter generator failure. The starting battery on a Generac Guardian, Kohler Residential, or Cummins QuietConnect is a sealed lead-acid or AGM unit that has the same characteristics as any 12V battery - it likes to be kept charged, it loses capacity in the cold, and it self-discharges if not maintained. A battery that read 12.6V in October may read 11.4V by late January, especially if the generator has not exercised in months.
What you hear: the controller display lights up, the start signal goes through, the starter motor either clicks once (battery has voltage but no cranking amps left) or cranks slowly and gives up before the engine catches. If the controller does nothing at all, the battery is below the cutoff voltage and the controller is not even trying.
The fix is a new battery. We carry the right group sizes for Generac, Kohler, and Cummins residential units. While we are there we test the charger inside the transfer switch panel - a generator with a faulty trickle charger ate its own battery, and a new battery will follow it within months if the charger is not fixed.
Failure two: oil thickened past the cold-weather rating
Every generator has an oil spec for ambient temperature. Most factory fills are 5W-30, which is fine down to about -15 to -20. At -25 and below, 5W-30 is starting to gel - thick enough that the starter motor struggles to crank the engine through compression. The engine cranks slow, the starter draws excessive current, and the controller cuts the start attempt before the engine fires.
Manufacturers spec a cold-weather oil for very cold climates. Generac's spec for Muskoka winters is 5W-20 below freezing, sometimes a synthetic 0W-30 for the coldest installs. Kohler and Cummins have parallel specs in their owner's manuals. The right oil should have gone in at the fall service - but a lot of fall services skip the oil change if the unit "looks fine."
The diagnostic is straightforward: a slow crank that gradually picks up speed as the cylinders pump some oil flow is usually the oil viscosity issue, not a battery problem. Battery weakness shows as slow-and-getting-slower. Oil thickness shows as slow-and-getting-faster.
Failure three: propane regulator freeze
A propane-fuelled generator can ice up at the regulator on the coldest days. The regulator drops tank pressure from 10-15 PSI down to the inches-of-water-column that the engine needs. Pressure drop produces cold (Joule-Thomson effect), and when ambient is already -25, the regulator surface can drop into the territory where any moisture in the line freezes inside the regulator and chokes off flow.
The pattern: the engine starts, runs for 5-30 seconds, then stumbles and dies. The controller logs a low-fuel or undervoltage fault. The owner walks out, the regulator is frosted over, sometimes with visible ice on the surface.
The fix has several pieces. The line from the tank to the regulator needs a moisture-removal step (a dedicated dryer or a longer copper run to allow condensation to drop out before the regulator). The regulator itself may need a winterizing cover. The tank fill should not have included any water. We coordinate with the gas fitter on the regulator side; we own the electrical side of the install.
Failure four: the unit has not exercised in three months
Standby generators have a programmed exercise cycle - typically a 10- or 12-minute run once a week at a specific day and time. The exercise circulates oil, keeps seals lubricated, keeps the battery topped up via the alternator output, and surfaces any problem under controlled conditions so the homeowner finds out before the storm.
The exercise can stop running for several reasons. The most common is that the program got cleared by a controller battery failure (older Generac units used a coin cell to hold settings). Other reasons include a transfer switch fault that left the unit "locked out" and a moisture-related controller fault that disabled the schedule.
The symptom is a no-start that surprises the owner because "the generator was new five years ago and I have never had a problem." A generator that has not run in 12 weeks has aging fuel in the regulator and carburetor, sticky valves, and a battery the alternator has not topped up - the failure has been building since the last exercise that actually ran. The fix is to clear the fault, reprogram the exercise, and run a load-bank or actual-load test to verify the unit will perform when called on.
Failure five: the automatic transfer switch faults
The generator can be perfectly healthy and still not run if the automatic transfer switch (ATS) does not signal it to start. The ATS senses utility loss, after a programmed delay signals the generator to start, after the generator stabilizes transfers the load from utility to generator, and on utility return transfers back.
Common ATS faults:
- Sensing failure. The ATS does not detect the utility outage - usually a control board failure or a sensing-circuit fuse blown.
- Stuck contactor. The mechanical contacts that switch the load have welded or seized. Often the result of a brownout where the ATS chatters back and forth.
- Communication fault with the generator. Wiring damage between the ATS and the generator control panel. Mice love this wire.
- Programmed delay too long. Some setups have a long stabilization delay set, and homeowners think the generator failed when really it was about to start.
The diagnostic is at the ATS panel - check the displayed state, check the controller error log, verify the sensing wiring, verify the signal to the generator. We carry the right replacement parts for Generac, Kohler, and Cummins ATS units when the fault is the contactor or control board.
The exercise that nobody does
The cheapest preventive maintenance is sitting in your driveway. Once a month, walk to the generator and watch the next scheduled exercise. Verify it starts, runs the full programmed duration, and stops cleanly. Listen for new noises. Watch for smoke (any black smoke past the first 30 seconds is a problem). The exercise that runs unobserved every Saturday for years is the one that quietly stopped working in October and nobody noticed.
What we do at annual service
An annual service catches almost everything above before it becomes a January call. Specifically:
- Oil and oil filter change, correct viscosity for the upcoming winter
- Air filter inspection and replacement as needed
- Spark plug inspection or replacement on units that use them
- Battery load test with a real load tester, not just a voltage reading
- Verification of the exercise cycle - watch it run for the full programmed duration
- Transfer switch test under live conditions - kill the utility at the meter and watch the ATS hand the load over
- Controller error log review
- Visual on the propane line, regulator, and venting
- Thermal scan on the alternator and transfer switch under load
Our standard generator service plan covers all of the above on a Generac, Kohler, or Cummins residential unit, with documentation. Our post on sizing standby generators for Muskoka covers what to buy in the first place; this post is what keeps the unit you already own running.
When to call us
If your generator did not start during the last storm, did start but tripped offline, or has not exercised in months and you are watching the forecast nervously, we run emergency generator diagnostics across Huntsville, Bracebridge, Gravenhurst, Hamilton, and Burlington. Same- or next-day during outage weeks. Request a service visit and tell us what you saw or heard at the unit - it speeds up the diagnosis.