The first time this happened, the pilot light on the water heater would just spontaneously go out, leaving us with cold water every couple weeks. The second time this happened, the pilot was staying lit, but the water just wasn't getting as hot as it should have. Looking through the pilot light window, we could see bright yellow flames instead of the desired blue flames, which is a sure sign that the heater wasn't getting as much combustion air as it wanted.
|Look through this window to check the flame color|
The first time this happened, a Kenmore customer support rep talked me through the cleaning process. The second time (a few years later), I remembered just enough about it to find the process with Google's help. This link will take you to an image which is a scanned article detailing the process.
Other brands or models of water heaters may be different, but here's how it works on our Kenmore Power Miser 12:
At the very bottom of the heater, there are two plastic covers that keep the dust bunnies out of the intake. Behind these is a cavity only about 1.5" (4cm) tall. The roof of this cavity is a perforated plate known as the "flame arrestor." All of the combustion air must come through the plastic grates and then up through the flame arrestor before getting to the burner. In dusty environments, like our basement floor, the flame arrestor can become clogged with fluff to the point where the burner is starved for air.
|The bottom of the arrestor visible in the mirror|
The first step is to turn off the water heater. Follow the manufacturer's instructions for your particular model. On mine, I turned the heat knob all the way down and then turned off the pilot light knob. The last thing you want is to suck the flame backward through the air intake.
Cleaning the arrestor is straightforward: just brush it with a household bottle brush while a vacuum cleaner sucks up the loose dust.
Unfortunately, the openings where the plastic grates sit are too small for my (and probably most) vacuum nozzles to pass, so I had to make a custom attachment.
I grabbed a box from the recycling bin and folded it into rectangular tube about 1/2" tall, 1.5" wide, and 16" long. I taped one end of the tube to the vacuum hose, and taped the bottle brush to the other end. This new tube was flat enough to pass through the openings underneath the water heater so that I could scrub the heat arrestor and vacuum up what fell off.
Once everything was clean, I turned the heater back on using the manufacturer's recommended procedure. It'll probably be printed on a safety label on the side of the heater.
This whole process took less than 30 minutes, and the water heater works as good as new after it's been done.
Questions? Comments? Rude remarks? Send them my way in the comments section below.