Controller displays F06 – Low coolant temperature alarm, generator will not accept load

Safety first: Isolate AC power to the jacket water heater before working on it. Verify the generator cannot start automatically.

• Check heater power: Verify that the coolant heater (block or immersion heater) is receiving the correct supply voltage from the standby power panel. Check the circuit breaker and any local disconnect.
• Inspect heater element: Feel the heater housing after it has been energized for some time; it should be warm. If it remains cold, test the element resistance with a multimeter and replace if open.
• Thermostat function: If the engine takes a long time to warm up or never reaches normal temperature, the thermostat may be stuck open. Replace the thermostat with an MTU-approved part.
• Sensor verification: Compare the controller’s displayed coolant temperature with an external thermometer at the thermostat housing. If readings differ significantly, replace the coolant temperature sensor.
• Re-enable load acceptance: Once coolant temperature is within the specified range, clear the F06 alarm and verify that the generator synchronizes and accepts load correctly.