Flame Guard and Flame Lock Gas Water Heaters are made by American Water Heater Company and sold under the names American Proline, Whirlpool, Envirotemp, Mor-Flo, Powerflex, Premier Plus, US Craftmaster and possibly others. The Flame Guard and Flame Lock are names for FVIR (Flammable Vapor Ignition Resistant) Technology designed and manufactured by American Water Heaters. FVIR is a required safety design on gas water heaters that includes a sealed combustion chamber with a flame arresting barrier on the combustion air inlet and a device that detects a taller burner or pilot flame and shuts off the gas supply to the burner. If flammable vapors enter through the flame arresting barrier they may burn as excess fuel in the burner area but the flame cannot flash back through the flame arrestor to the source of the vapors preventing fire and explosion. Older styles of water heaters without the FVIR Technology could be an ignition source for flammable vapors, possibly causing and explosion and fire if a flammable liquid was spilled nearby.
There are a lot of possible problems with water heaters many of them quite generic which will not be covered in this trouble shooting guide. The focus will be on problems specific to the Flame Guard and Flame Lock design water heaters.
Early models of the Flame Guard and Flame Lock Water Heaters had a specially designed thermocouple that included a one time use thermal fuse that was designed to trip when a taller than normal flame occurred. These thermocouples were unusual in that they had a thermal fuse in addition to the usual flame detection function and they had a left handed thread to prevent the substitution of a regular thermocouple. The availability of these unique thermocouples was limited to a limited supply at Lowes and through American Water Heaters. The poor supply of replacement thermocouples with a fee for shipping and handling from American Water Heaters resulted in a Class Action Suit and Settlement where owners were supplied with a “Enhanced Burner Assembly” which included a new combustion chamber door, pilot/thermocouple assembly, burner assembly, and a thermocouple adapter. The models included in this suit have a round sight glass in the burner door and have serial numbers beginning with “FG” and “FL” and were manufactured between 2000 and 2006. Water heaters manufactured after 2006 have the “Enhanced Burner Assembly” already installed and have a serial number starting with a “B” The Class Action Settlement Period ended June 28, 2008.
The “Enhanced Burner Assembly” fixed the problem with the one time use thermocouple by using a resettable thermocouple which screwed into a thermocouple adapter. The thermocouple adapter screws into the left hand threads where the original thermally fused thermocouple screwed into the gas valve. Instead there is a reset button in the door of the burner assembly and 2 wires which connect to the thermocouple adapter.
The basic problem in most cases is a lack of combustion air caused by the screen of the air inlet on the bottom of the water heater. Frequent cleaning of this screen is required to avoid trouble. When the burner becomes starved for air the flame gets taller just like it would in an FVIR event and causes the sensor to trip. Some of the kits along the way also included a prefilter that wraps around the base of the water heater. If you have one of these keep it clean as well. Many people have luck making up a piece of pipe with an elbow on it to attach on the end of a vacuum cleaner hose to vacuum clean the screen under the water heater.
If cleaning the flame arrestor screen under the unit does not cure the problem there may be other problems relating to draft, insufficient combustion air, negative air pressure in the building or another problem in the unit that is best left to a licensed plumber.