The short answer
When a Rheem gas furnace in Northern Virginia won’t ignite, the board says so: code 11 on a two-digit display, 4 red blinks on an older board, or 1 green blink after four failed tries. If it lights and then goes out, that’s 13. The usual causes, in the order we find them: a dirty flame sensor, a cracked igniter, the gas turned off, or a vent or drain problem that keeps the pressure switch open so the igniter never gets its turn.
How a Rheem lights
Every call for heat runs the same order. The inducer fan starts and pulls air through the burners. The pressure switch closes once that draft is there. The igniter glows orange. The gas valve opens and the burners light. The flame sensor proves the flame within seconds, or the valve closes again. Then the blower comes on. Where it stops tells you what failed.
The $67 Heating Check
We check your furnace, heat pump or boiler before winter. Through December 31. See the offer
What you see, and what it points to
Swipe to see all columns →
Swipe to see all columns →
| What you see | What it points to | Code you’ll likely see |
|---|---|---|
| Nothing at all | Power, the furnace switch, the door switch, a blown fuse | None, or 30 |
| Inducer runs, igniter never glows | The pressure switch isn’t closing: vent, drain, hoses | 45, 2 red, 2 green |
| Igniter glows, no flame | Gas off, the gas valve, a weak igniter | 11, 4 red, 1 green |
| Lights, then goes out in a few seconds | The flame sensor, the ground, reversed wiring | 13, 12, 26, flashing yellow |
| Runs a while, then shuts off | Overheating from low airflow, or the rollout switch | 22, 33 |
How many times it tries
A two-digit Rheem tries four times, then locks out for an hour and alternates 10 with 11. A board with one green light also gives up after four tries and blinks once; Rheem says cutting power or turning the thermostat off for 5 to 10 seconds clears it. Our reset guide covers how, and why one reset is the limit.
What you can safely check
- Set the thermostat to heat and a few degrees warmer than the room. Swap its batteries if it has them.
- Find the furnace switch, which looks like a light switch on or near the furnace, and make sure it’s on. Check the breaker.
- Make sure the lower door is seated. It presses a switch, and a loose door means no power.
- Find the gas valve handle on the pipe into the furnace. In line with the pipe is on.
- Try another gas appliance. If the stove won’t light either, call your gas company: it’s the supply, not the furnace.
- Change the filter and clear the PVC pipe ends outside.
- Reset once and watch through the window: inducer, glow, flame, blower.
What not to do
Don’t touch the igniter. It’s brittle and cracks easily, and a cracked one is the reason a lot of furnaces stop lighting. Cleaning a flame sensor is a common fix, but it means pulling the burner door and working beside the gas valve, so it’s our side of the furnace. Never jump or bypass a safety switch to get heat back. Each one is there to stop the furnace from burning gas when something is wrong, and the wrong thing is often exhaust, which carries carbon monoxide. If your carbon monoxide alarm goes off, get everyone outside first and read our CO alarm guide from there. If you smell gas, don’t flip any switches: leave the house and call your gas company or 911 from outside.
What a technician does
We watch a full ignition sequence with the doors off and read the fault history. Then we measure: microamps at the flame sensor, the igniter’s resistance, gas pressure at the valve (about 3.5 inches of water column on natural gas, about 10 on propane), whether the flame carries across every burner, and the ground and polarity at the board. Most no-ignition calls end with a clean sensor or a new igniter the same visit, and you get the price before we start.
Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. It covers the flame sensor, the igniter and gas pressure before the first cold night.
Related: flame sensor video, flame sensor problems, Rheem furnace codes, furnace won’t turn on and every brand in our error codes guide.
Every code meaning here comes from Rheem’s own documents: R96V manual, RA 80+ manual and furnace FAQ.
Call or book
A repair visit starts with a flat $99 diagnostic, or $250 after hours, and you get the price of the fix before we touch anything. Call (703) 997-9757, day or night, and tell us the code you counted, or book online from goswiftpro.com/cookiesoffer by November 30 and a box of warm MOLTN cookies comes with the heating check. Every current deal is on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why does my Rheem furnace igniter glow but not light?
The board opened the gas valve and no flame came, or the flame came and the sensor didn’t see it. Check that the gas valve handle is in line with the pipe. If it is, the usual cause is the flame sensor, the gas valve or low gas pressure.
Why does my Rheem furnace light then shut off?
If it goes out in a few seconds, the flame sensor isn’t proving the flame: a dirty sensor, a poor ground or reversed wiring. If it runs for minutes first, look at the filter and the vents: that’s usually overheating.
How many times will a Rheem furnace try to light?
Four. A two-digit board then locks out for an hour and alternates 10 with 11. A single green light blinks once for a soft lockout.
Can a dirty flame sensor stop a Rheem furnace from lighting?
It’s the most common reason a Rheem lights and then shuts off within seconds. The board shuts the gas if it can’t see the flame, and a coated sensor can’t.
