Firman Generator Shuts off After 20 Minutes (How to Fix)

If you own a Firman generator, you may have encountered an issue where it shuts off after running for approximately 20 minutes.

This problem can be particularly frustrating, especially if you are relying on your generator for power during an outage or for powering important appliances and equipment.

There are several possible reasons why your Firman generator may be behaving this way, and in this guide, we’ll explore these potential causes and provide practical solutions to get your generator running smoothly again.

So, if your Firman generator keeps turning off after 20 minutes of operation, keep reading to gain valuable insights on how to fix it.

Firman Generator Shuts off After 20 Minutes

Firman Generator Shuts off After 20 Minutes

1 . Overloaded Circuit Breaker

An overloaded circuit breaker is one of the common causes for a Firman generator shutting down after about 20 minutes of operation.

This usually happens when the generator is burdened by more appliances than it can handle.

Consequently, an excess of electrical load is placed on the generator, causing the circuit breaker to trip as a protective measure.

This overload can result in the generator shutting off to prevent damage to its internal components. Remember, your Firman generator has a maximum load capacity that shouldn’t be exceeded.


The solution to an overloaded circuit breaker is a simple one – reduce the load on your Firman generator.

Start by identifying and disconnecting non-essential appliances or equipment that are currently running on the generator.

Once the load is appropriately reduced, reset the circuit breaker by switching it to its “ON” position.

Please ensure that you do not exceed the rated capacity of your generator to prevent future occurrences.

2 . Insufficient Fuel Supply

The primary reason why a Firman generator might shut off after running for 20 minutes could be an insufficient fuel supply.

This typically happens when the generator’s fuel tank is not filled to the required level.

Running a generator on low fuel can cause the engine to overheat, leading to automatic shutdown as a safety measure.


The simplest solution for this issue is to ensure your generator’s fuel tank is adequately filled before use.

Regularly check the fuel level, especially if you plan to run the generator for an extended period.

In a situation where the generator continues to shut off despite having sufficient fuel, it might indicate a more serious issue, such as a faulty fuel gauge or problems with the fuel delivery system.

3 . Faulty Spark Plug

A faulty spark plug can cause your Firman generator to shut off after 20 minutes. The spark plug is an essential component that creates the spark necessary to ignite the fuel-air mixture in your generator’s engine.

If the spark plug is faulty or worn out, it will not be able to produce a strong enough spark, causing the engine to run unevenly or shut off prematurely.

A significant sign of a faulty spark plug is when your generator runs fine initially but then suddenly shuts off.


The solution to a faulty spark plug is relatively straightforward – replace it.

You need to first locate the spark plug, which is typically near the back of the generator. Unscrew the old spark plug and replace it with a new one.

Ensure you have the correct spark plug for your Firman generator model.

After replacing the spark plug, run the generator again to see if the issue is resolved.

4 . Blockage in the Air Filter

A blockage in the air filter can cause your Firman generator to shut off after running for about 20 minutes.

When the air filter is blocked or dirty, it can prevent the necessary air from reaching the combustion chamber.

This can cause the engine to overheat and subsequently shut down as a safety mechanism to prevent damage.


The solution is rather straightforward.

You need to check the air filter for any blockage or dirt. If it’s dirty, you can clean it with a soft cloth and mild detergent

However, if the filter is significantly blocked or damaged, it would be safer to replace it with a new one.

5 . Engine Overheating

Overheating of the Firman generator engine can result from various factors such as lack of coolant, mechanical issues, or even a faulty thermostat.

An overheated engine can cause the generator to automatically shut off after approximately 20 minutes of operation.

This automatic shut-off is a safety feature built into the generator to prevent damage to the engine and other components.


To prevent engine overheating, regular maintenance is crucial.

Firstly, ensure that the coolant level is adequate. If the coolant level is low, it might not be able to efficiently cool down the engine.

Aside from that, it’s also important to check for any mechanical issues or malfunctioning components such as the thermostat

If the thermostat is faulty, it won’t properly regulate the engine’s temperature, leading to overheating


In conclusion, a Firman generator shutting off after about 20 minutes of operation can be due to various reasons, such as blockage in the air filter or engine overheating.

Regular maintenance and periodic checks can help identify these issues early and prevent unexpected shutdowns.

Always ensure that the air filter is clean and free from blockages and that the engine is not overheating due to inadequate coolant levels or a faulty thermostat.

Frequently Asked Questions

How often should I check the air filter of my Firman generator?

It’s recommended to check the air filter every month and clean or replace it as necessary.

What can cause the Firman generator engine to overheat?

Lack of coolant, mechanical issues, or a faulty thermostat can cause the engine to overheat.

What should I do if my Firman generator shuts off after 20 minutes?

Check if the air filter is blocked and whether the engine is overheating due to inadequate coolant or a faulty thermostat.

How can I prevent my Firman generator from shutting off unexpectedly?

Ensure the air filter is clean and the engine is not overheating.

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