The sequence: inducer proves draft, igniter heats, gas valve opens, flame sensor confirms. Code 11 says the confirmation never arrived. Rheem's own literature ties 11 to the lockout math: four failed ignitions in a row and the control enters its one-hour lockout, alternating 10 and 11 on the display — so a Rheem flashing between two numbers is showing you this code and its consequence together.
Your checks are the ignition basics: the thermostat is really calling for heat, the gas shut-off at the furnace is open (the classic post-summer, post-service miss), the filter is not strangling anything, and one — one — reset to watch a full attempt. A furnace that glows, clicks, and never catches has told you the igniter or the gas side needs hands, not retries.
Homeowner checks — the safe list:
- Thermostat set to Heat, and set a few degrees above the room temperature.
- The gas shut-off valve at the furnace: handle in line with the pipe means open. If it is off, that is your answer — and ask yourself why it was off.
- Air filter: pull it and look. A matted filter causes more furnace faults than any broken part.
- One reset is fair: power off at the switch for 30 seconds, back on, and watch what it does. If it locks out again, stop resetting it — the code is telling you something real.
11: Failed ignition
Homeowner checks
The ignition attempt did not produce proven flame. Start with the gas supply and the thermostat call; the igniter and sensor are a tech’s check.
From the table: 7-segment display codes (no blink counting) — source: Rheem 95P Series Installation Instructions, "Diagnostics and Fault Codes" (read the document, fetched 2026-10-30). Covers: Rheem 95P-series and the R801T generation: the control has a small digital display. Standby reads 0; running modes read as letters. Faults show as two-digit numbers, first digit for a second, second digit for a second, then a pause.
11 versus 12 and 13
Rheem splits flame failure into three codes and the split is diagnostic gold: 11 never lit. 13 lit, then lost the flame mid-cycle. 12 has flame but the signal is too weak to trust. If yours sometimes runs for a minute before quitting, you are probably counting a 13's story — tell the technician the behavior, not just the number you caught.
The two rules that outrank everything on this page.
1. Smell gas? Stop reading. Leave the house and call your gas utility or 911 from outside. No code is worth diagnosing through a gas smell.
2. Never bypass a safety switch — no jumping a pressure switch, no taping a limit, no propping a rollout. Those switches are the only thing between a furnace fault and a fire or carbon-monoxide problem. This library explains codes; it does not teach repairs inside the cabinet.
One honesty note before the tables: codes change between control boards, sometimes inside the same brand and the same decade. Every table below names the board and the manual it was transcribed from. The chart glued inside your own blower door is the final word for your furnace — if it disagrees with this page, believe the door.