Fire extinguishers need to be regularly checked to ensure that:
The extinguisher is not blocked by furniture, doorways, or any thing that might limit access in an emergency.
The pressure is at the recommended level. Some extinguishers have gauges that indicate when the pressure is too high or too low.
All parts are operable and not damaged or restricted in any way. Make sure hoses and nozzles are free of insects or debris. There should not be any signs of damage or abuse, such as dents or rust, on the extinguisher.
The outside of the extinguisher is clean. Remove any oil or grease that might accumulate on the exterior.
Shake dry chemical extinguishers once a month to prevent the powder from settling or packing. Check the manufacturer's recommendations.
Pressure test the extinguisher (a process called hydrostatic testing) after a number of years to ensure that the cylinder is safe to use. Find out from the owner's manual, the label, or the manufacturer when an extinguisher may need this type of testing.
Immediately replace the extinguisher if it needs recharging or is damaged in any way.