Not all Rheem water heaters have pilot lights, and if yours doesn't, the procedure for how to turn on the water heater doesn't include relighting the pilot. Some Rheem models have other ignition systems, such as spark ignition modules and hot surface ignition modules. These don't work in exactly the same way, but all you need to know is that if your water heater is equipped with one and the water is cold, there's either a problem with the electricity (perhaps the breaker has tripped) or the module is faulty and needs to be replaced.
If your Rheem water heater does have a pilot, you'll see a dial and a button on the gas module on the front of the tank. There's also a small window at the bottom of the tank through which you can observe the pilot, although it may be covered by a plate that you can remove. Sometimes, there's also an LED on the gas module that blinks at regular intervals when the pilot is on. If your water heater has this LED and it isn't blinking, it's a sign to relight the pilot.
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How do you light a Rheem water heater pilot? Here's what to know.
Before You Turn On the Water Heater
Gone are the days when you could relight pilots with a long match. Most modern gas water heaters have sealed combustion chambers, and the only way to light the pilot is to use the piezoelectric spark generator, which is activated by the button on the gas module.
Whether or not your water heater has an LED, it's a good idea to remove the cover plate from the front of the tank so you can see the pilot window. You may have to lie on the floor to get a good look, but you'll be able to verify not only that the pilot has come on but that the burner lights when you set the temperature control immediately after lighting the pilot. A weak pilot or failure of the burner to ignite could signify issues with the gas supply, and you should get a pro to check that.
How to Relight the Pilot
Before you relight the pilot, check the gas valve to make sure it's on (the handle should be parallel to the gas pipe), turn the gas valve on the front of the tank to the "off" position, and wait five minutes for any residual gas to clear out. Turn the dial to "pilot," push it in, and hold it while you repeatedly press the spark ignition button. If the unit has no LED, you'll have to look through the window to see the pilot, and doing this while you push the button and hold down the dial can be challenging, so you may want to get someone to help.
It usually takes several pushes of the button to get the pilot to ignite — sometimes as many as 20 — so be persistent. When you see the pilot flame or the LED lights up, keep holding in the button for about 20 seconds. This gives the thermocouple, which is an electrical device that detects the heat of the flame, time to warm up. If you release the button prematurely, the pilot will go out. If the pilot stays on when you release the dial, turn it to "on" or to the desired temperature depending on the model.
Problems With the Pilot
You may notice that no matter how long you hold in the dial, your Rheem water heater pilot light won't stay lit. This is usually caused by a worn-out thermocouple. You can buy a replacement thermocouple and install it yourself, but the fact that the chamber is sealed adds an element of complexity that didn't exist when you had easier access to the combustion chamber, so you may want to hire out this job.
You may also notice that the pilot is weak and burns with an orangish glow; a healthy pilot burns blue and is about an inch high. A weak pilot probably won't stay lit for long, and this is probably the reason you're now having to relight it. The problem is often soot or some other contamination in the pilot tube. Because the chamber is sealed, you may want to call a pro to clean it.