If you bought a water heater in the last few years, you may have some homework to do. About 616,000 Ultra-Low NOx water heaters produced between April 2011 and August 2016 have been recalled due to a potential fire hazard, and need to be evaluated and repaired as soon as possible. These water heaters are either 30, 40, or 50 gallons and use either propane or natural gas.

The majority of these appliances were sold in California, but it’s a good idea to check your water heater no matter where you live. The recalled appliances were sold under a number of different brand names (American, A. O. Smith, Kenmore, Reliance, State, U.S. Craftmaster and Whirlpool) and by a variety of vendors including independent contractors, plumbers, and home improvement stores. They originally cost between $500 and $1,000.

These water heaters pose a potential danger when the gas burner tears and causes the appliance to produce excess radiant heat. When that heat comes in contact with a wood floor or any other combustible material, it could cause a fire. So far there have been six fires, all when the water heater was installed on a floor made of combustible material. Luckily no one has been injured yet.

If you think your water heater may be included in the recall, the first step is to check the serial number. You can find it on the data plate next to the gas control valve or thermostat. If the first four digits are not between 1115 and 1631, you’re in the clear. If they are, you’ll need to investigate further.

If you think this recall might apply to you, head to www.waterheaterrecall.com and enter the serial number. You can also call if you prefer.

Once you’ve confirmed that your water heater is included in the recall, the first and most important step is to turn off the water heater and refrain from using it until you’re sure it’s safe. Then contact A.O. Smith to discuss your free repair.