Why generators fail to start — and the five-minute check that catches most of it

The generator that fails to start on the night of the storm is not usually a broken generator. It is usually a maintained generator that missed one thing — a battery, a switch, a fuel valve — and the failure was visible for weeks before the storm, to anyone who looked. This page is the list of the reasons, in the order they actually happen, and the check that catches most of them in five minutes.

The short answer

The most common reason a standby generator fails to start is the battery. Not the engine, not the fuel, not the electronics — the battery. A standby generator’s battery is a small car battery, sitting in a hot enclosure, in Florida, for months at a time. It degrades quietly, it shows a healthy voltage right up until it cannot turn the starter motor, and it is the first thing a technician checks when a generator will not start. Replace it about every three years, on a schedule, whether it looks fine or not.

Figures last reviewed November 2026 · Sources: manufacturer service guidance (Generac, Kohler); Palm Beach County-area service pricing — see “How we get our numbers” on the About page.

1. The battery is dead or dying

The battery is the number one cause, and it deserves the detail. A standby generator’s starter battery is charged by the generator itself — when the generator exercises, the charger tops the battery up. If the generator has not exercised — because the exercise schedule was disabled, or because the battery was already too weak to start the exercise — the battery drains further, and the spiral continues. The signs are visible before the failure: a missed exercise in the monitoring app, a battery voltage that is falling week by week, a start that is slower than it used to be. A battery costs about $200 or more to replace. A generator that will not start on the night of the storm costs considerably more than that — in the house it was supposed to protect.

What to do: replace the battery about every three years, on a schedule. Check the monitoring app weekly for missed exercises and falling voltage. If the generator has not exercised in a month, do not wait for the storm to find out why.

2. The generator is not in automatic mode

The control panel has a switch: automatic, manual, off. If it is in manual or off, the generator will not start when the power goes out — no matter how new the battery, how full the fuel, how perfect the engine. Somebody has to have moved it: a technician who forgot to put it back after a service visit, a house-sitter who was curious, a homeowner who turned it off for the summer and forgot. It is the easiest failure to prevent and the most embarrassing to discover. The monitoring app shows the mode — which is why the first thing the app tells you matters. The snowbird’s checklist puts “confirm automatic mode” first on the departure list for exactly this reason.

3. The fuel is not getting there

On a natural gas unit, the fuel supply is the utility’s, and it rarely fails. What fails is the connection: a shutoff valve that was closed during a service visit and never reopened, a regulator that has failed, a line that has been damaged. On a propane unit, the failure is simpler: the tank is empty, or the gauge was misread, or the tank was at 30% when the season started and nobody filled it. A generator that runs out of fuel mid-outage is a generator that was not fuelled — and the fuel maths is the owner’s responsibility, not the installer’s. The propane vs. natural gas page covers the runtime numbers: how long a tank lasts, and how to size it.

4. The oil is low, or the oil is old

A standby generator will not start — or will shut itself down seconds after starting — if the oil is below the minimum, or if the oil pressure sensor has failed. Low oil is a protection, not a fault: the engine is protecting itself from destroying itself. Old oil is a slower problem: it loses its ability to lubricate, and the engine wears faster, and the starts get harder. The annual service visit changes the oil and the filter. A generator that has not had its oil changed in two years is a generator that is being asked to start on oil that has been sitting in a hot engine compartment for two years. Change it annually, whether the generator ran or not.

5. The exercise cycle was disabled — or never set

A standby generator exercises itself weekly, for a few minutes, to keep the battery charged and the engine lubricated. If the exercise was disabled — because the noise annoyed a neighbour, because somebody thought it was wasting fuel, because a technician turned it off and forgot — the battery slowly drains, the engine sits, and the first time the generator is asked to start is the night of the storm. Confirm the exercise is enabled, and note the day and time it runs, so a missed exercise is noticeable. The monitoring app logs every exercise. A week with no exercise is a week to call somebody.

6. A fault the controller already knew about

The generator’s controller logs faults: overcrank (it tried to start and could not), low oil pressure, overspeed, undervoltage, a sensor that has failed. A fault that is logged and ignored is a failure waiting for a storm. The monitoring app shows faults as they happen. A fault code you do not recognise is a reason to call a technician — not a reason to clear the code and hope. Clearing a fault without fixing it is like turning off a smoke alarm without checking for a fire.

7. The transfer switch did not transfer

The generator can start perfectly and still leave the house dark, if the transfer switch — the device that switches the house from the grid to the generator — does not work. A transfer switch can fail mechanically, or its control wiring can be damaged, or it can simply not have been tested since installation. The annual service visit tests it: power cut, generator starts, load carried, power restored. A service visit that does not test the transfer switch has not tested the system. If your generator has never had its transfer switch tested, book a visit.

The five-minute check

Once a month, in five minutes, you can catch most of the failures on this page:

1. Open the monitoring app. Did the generator exercise this week? Is the battery voltage steady? Is there a fault logged?
2. Walk outside. Is the generator in automatic mode? Is the panel clear — no warning light, no error message?
3. Look at the fuel. Propane: is the tank above half? Natural gas: is the shutoff valve open?
4. Listen to the next exercise. Does it start promptly, run smoothly, and sound the same as it always has?
5. If anything on this list is wrong — a missed exercise, a falling voltage, a warning light, a rough start — call a technician. Not next month. Now, while the weather is calm.

Five minutes, once a month, is the cheapest insurance a generator owner can buy. It is also the check that most owners never do — which is why most failures are surprises.

Related: Remote monitoring · Maintenance & service plans · What size generator does my house need?

Palm Beach Backup Power is an information and matching service — we do not install generators. We do not take a fee from you. Our installer partner pays us when a consultation they receive through us becomes an installed generator. The price you pay is the installer’s price either way.