How to Light a Rheem Classic Professional Water Heater

Smell for Gas Near the Floor Before Doing Anything

Standing in front of a cold water heater is frustrating when you need hot water right away. Before touching any controls on your tank, you must confirm the space is safe. Gas appliances run reliably for years, but trying to light a pilot flame when unburned gas lingers in the air creates an immediate hazard.

Natural gas is lighter than air and rises, while propane is heavier than air and sinks across the floor. Gas suppliers add mercaptan, a chemical smelling like rotten eggs or sulfur, so you can detect even tiny leaks. Bend down and sniff at floor level around the base of the heater, behind the tank, and in nearby corners. If you smell even a faint sulfur odor, step away immediately, leave your home, and call your gas provider from outside.

Inspect the space around your tank. Water heaters draw combustion air from around the base, so the floor must stay clear of debris and fumes. Solvents, paint cans, gasoline jugs, and rags should never sit near a fuel-burning tank. If your water heater sits in a drafty garage, pairing the room with an electric heater for garage with thermostat can keep ambient temperatures steady and prevent freezing pipes during cold snaps.

Run through this quick safety checklist before touching the controls:

• Sniff close to the floor and along the gas fittings for any sulfur or rotten egg smell.
• Check the manual shutoff valve to confirm the handle runs parallel to the pipe, meaning the fuel is turned on.
• Clear away combustible items, paper, cardboard, and stored liquids within three feet of the burner base.
• Wait at least 10 full minutes with the control dial set to OFF if someone tried lighting the tank earlier.

Follow the Sparker Sequence to Ignite the Pilot Safely

Lighting a Rheem Classic Professional water heater requires no matches or lighters. These units use a sealed combustion chamber that prevents open flames from contacting dust or vapors in your home. You manage the lighting process from the outside using the main gas dial box on the tank front (the gas control valve) and a push-button sparker (a small button that creates an internal electric spark when clicked).

Follow these sequential steps to ignite the pilot flame:

1. Lower the temperature dial: Turn the temperature dial on the front of the gas valve to its lowest setting, typically labeled VACATION or very low. This prevents the main burner from firing up unexpectedly the instant the pilot catches fire.
2. Turn the gas knob to OFF: Turn the main gas control knob on top of the valve clockwise until it points to OFF. If an earlier lighting attempt failed, pause here and wait 10 minutes so unburned fuel can clear out through the chimney flue.
3. Switch the knob to PILOT: Rotate the control knob counterclockwise to align with PILOT. In this position, the internal spring mechanism allows you to push the knob down into the valve housing.
4. Press and hold the knob down: Push the gas control knob down firmly. Depressing this knob manually opens an internal bypass valve that feeds a tiny stream of gas directly to the pilot burner while keeping the main gas supply shut.
5. Click the push-button sparker: While holding the knob down, use your other hand to press the push-button sparker repeatedly. Strike the button once every second or two, listening for a crisp click with each press.
6. Look for the flame: Peer through the small glass viewing window (a clear sight glass located on the lower metal access door). Look for a tiny blue flame to catch on the pilot bracket near the spark tip.
7. Hold the knob for 30 to 60 seconds: Once the pilot lights, keep holding the knob down. This gives the heat sensor time to warm up and produce the small electrical charge needed to keep the valve open on its own.
8. Release the knob and set to ON: Let go of the control knob slowly. If the pilot flame stays lit, turn the knob counterclockwise to the ON position.
9. Set your water temperature: Turn the temperature dial back up to your preferred warmth, typically at the recommended setting mark (around 120 degrees Fahrenheit). You will hear a soft whoosh as the main burner lights up.

Check the Glass Window and Blinking Status Light

Always verify that the flame burns cleanly before closing the closet door or walking away. Rheem Classic Professional tanks include a small glass viewing window (sight glass) built into the lower burner cover. Because this window sits low to the floor, you might need to kneel down and shine a flashlight through the glass to inspect the flame clearly.

Pay close attention to flame color and shape. A properly running pilot produces a steady, sharp cone with a deep blue body and a lighter blue tip. That tip should wrap smoothly around the upper third of the heat sensor. If the flame looks floppy, burns yellow, or flickers wildly, the burner may be starved for air or choked with lint. A yellow flame produces soot, which quickly coats internal parts and causes the pilot to fail.

Many Rheem Classic Professional models feature an electronic control box with a small status light. This light uses no wall plug and needs no batteries; it runs entirely on millivolt power generated by the heat of the pilot flame. Once the pilot flame has burned steadily for 30 to 60 seconds, this light will begin flashing.

Observe the blinking light to confirm the system status:

• One green flash every three seconds: This signals normal operation. The valve detects adequate heat, safety switches are closed, and the tank is ready to fire up the main burner.
• No flashing light at all: Either the flame has gone out, or the heat sensor has not reached operating temperature yet. If the flame is visibly burning but the light never flashes, the sensor may be dirty or misaligned.
• Rapid repeating flashes: A repeating pulse pattern (such as two, four, or five flashes) indicates an active safety lockout from a blocked air intake, low gas pressure, or an overheating chamber. Check the diagnostic sticker on the valve to match the flash pattern to the specific code.

Warm the Heat Sensor and Purge Line Air

The most common issue when lighting a water heater is that the pilot flame goes out the second you release the control knob. You hold the knob down, click the sparker, see the flame catch, but letting go instantly kills the fire. This is almost always caused by the thermocouple (a heat sensor that keeps gas flowing by creating a tiny electrical voltage when hot).

The heat sensor serves as an automatic safety guard. It contains two dissimilar metals fused inside a small rod placed directly in the pilot flame. When heated, these metals create roughly 20 to 30 millivolts of electricity. That tiny charge powers a miniature electromagnet inside the main gas control box, holding an internal valve open. If you release the knob after only a few seconds, the sensor remains lukewarm. The electromagnet drops, a spring snaps shut, and fuel cuts off instantly so raw gas cannot leak into your home. Holding the knob down for a full 60 seconds gives the sensor time to reach full operating heat.

Trapped air inside the fuel line is another frequent reason why the pilot refuses to stay lit. When a gas line has been shut off for plumbing work, or after an empty propane tank is refilled, the empty pipe fills with air. The sparker can click dozens of times without fire because pure gas has not reached the pilot tip. Manufactured homes often have strict ventilation and clearance rules for water heating closets, similar to the space demands you see when choosing a heater for mobile home utility areas, and clearing air lines in those tight quarters requires patient care.

To purge trapped air safely without wearing out the spark button, follow this method:

• Turn the gas control knob to PILOT and press it down firmly without clicking the push-button sparker.
• Hold the knob down steadily for roughly 60 to 90 seconds, letting gas pressure push the stagnant air bubble out through the pilot tube.
• Once the air pocket clears and fresh gas reaches the tip, click the spark button once every two seconds while keeping the knob depressed.
• The pilot flame should catch quickly once fresh fuel arrives at the burner bracket.

Lint and dust can also stop the pilot from staying lit. Because water heaters pull air from floor level, pet hair and dust collect on the bottom intake screen. If the burner lacks combustion air, or if soot coats the heat sensor, the sensor cannot reach the temperature required to keep the valve open. Wiping the base screen clean with a dry cloth often restores proper airflow and lets the flame heat the sensor reliably.

Shut Off the Supply Line When Specific Warnings Appear

While relighting a pilot flame is standard household maintenance, you must always handle fuel gas with care. Forcing an appliance to light when mechanical parts have failed can result in dangerous gas leaks, carbon monoxide issues, or fire hazards. If you follow the lighting sequence two or three times and the flame refuses to catch, stop and check for warning signs.

Do not attempt to relight the heater if you notice any of these serious red flags:

• A strong odor of sulfur or rotten eggs that lingers after waiting 10 minutes with the valve set to OFF.
• The push-button sparker feels loose, jammed, or fails to make a sharp clicking sound when pressed.
• Heavy black soot, blistered paint, or heat scorch marks appear on the outer burner cover plate or nearby walls.
• The main burner ignites with a loud boom, thumping sound, or a flash of flame puffing out from underneath the base.
• The status light blinks an error code indicating that the high-temperature safety switch has tripped.
• The control knob feels seized, cracked, or smells of raw gas directly around the dial stem.

If you spot any of these warning signs, shut down the water heater completely. Turn the gas control knob clockwise to OFF. Next, locate the manual shutoff valve on the pipe leading into the tank. Turn the valve handle a quarter-turn until it sits perpendicular (crosswise) to the pipe. This physically closes the pipe and blocks all incoming gas flow.

Never attempt to remove the sealed burner door, bend internal gas lines, or bypass safety controls on your own. A licensed plumber or your local gas utility technician has the proper pressure gauges, replacement parts, and training to repair gas controls safely. Calling in a professional ensures your hot water returns quickly without putting your household at risk.