1800 — Generac 1800 — Overvoltage
Alarm 1800 is Overvoltage: the generator output voltage rose above the rated value (roughly 10% over for a set period) and the controller shut down to protect connected equipment. It is NOT a low-battery code (low battery is a separate warning, code 2750). (Meaning corrected against official Generac support documentation / Evolution controller e-code list; older Nexus controllers may differ — confirm for your unit.)
- Keep using it?
- Limited use only
- DIY difficulty
- Moderate
- Verified against
- support.generac.com ↗
How to fix it
- This is a high-voltage electrical fault best handled by a Generac dealer/technician.
- Have the voltage regulator and excitation circuit tested.
- Confirm engine speed is within spec.
Why it happens
Typical signs: Shutdown shortly after starting · 1800 / Overvoltage in the alarm log · Possible over-voltage to the home before shutdown
- Voltage regulator fault Failed regulation driving output too high.
- Excitation / field winding issue Over-excitation raises output voltage.
- Engine overspeed High RPM raises output frequency and voltage.
More Generac generator codes
Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: support.generac.com.