Richmond error code 12 indicates an ignition failure — the unit attempted ignition but the flame sensor didn't detect flame within the safety timeout window. Distinct from code 11 (gas valve communication), code 12 specifically means the spark fired or pilot was lit but no flame establishment was sensed.
What triggers code 12
The control sequence attempts ignition (sparks the igniter, opens the gas valve), expects the flame sensor to confirm flame establishment within a typical 4-second window. Code 12 fires when this confirmation doesn't arrive — could be genuine no-ignition or sensor failure during what was actually a successful ignition.
Diagnostic steps
- Verify ignition attempt: with the front panel removed and the unit calling for heat, watch the ignition sequence. Listen for spark clicking, see if the burner attempts to light.
- If no spark: the igniter or ignition control module has failed. Replace igniter ($40–80) or test ignition module.
- If spark but no flame: gas isn't reaching the burner. Check that the gas valve is actually opening (code 11 diagnostic applies), verify gas line pressure under demand, check for blocked burner orifice.
- If flame visible but code 12 still triggers: the flame sensor is failing to detect flame. Clean the flame sensor with fine emery cloth or 400-grit sandpaper. Verify sensor is positioned in the flame path (about 3/8" into the flame zone).
Common causes of code 12
- Dirty flame sensor: the most common cause. Sensor accumulates oxidation and carbon over time, reducing its conductivity. Clean restores function.
- Failed igniter: hot-surface igniters degrade over time, eventually fail to glow hot enough. Spark igniters can crack or fail to spark.
- Insufficient gas pressure: under load, gas pressure drops below the minimum needed for stable flame. Static pressure may be fine but dynamic (during demand) drops too low.
- Blocked burner orifice: spider webs, dust, debris in the orifice prevents proper gas/air mixture.
- Cracked heat exchanger or burner manifold: rare but possible after many years of service. Allows combustion gases to disturb flame stability.
Flame sensor cleaning procedure
- Turn off gas and power to the unit
- Locate the flame sensor (typically a metal rod extending into the burner area)
- Disconnect the sensor wire (usually a single wire connector)
- Remove the sensor from its mounting bracket
- Polish the sensor rod with fine emery cloth or 400-grit paper, both sides
- Wipe clean with a dry cloth
- Reinstall in the original position with tip in flame path
- Reconnect wire, restore gas and power, test ignition
Gas pressure diagnosis
If flame sensor cleaning doesn't resolve code 12, measure gas pressure under load. Connect a manometer to the gas valve test port:
- Static (no demand): natural gas should read 7" WC inlet, 3.5" WC at burner. LP should read 11" WC inlet, 10–11" WC at burner.
- Dynamic (full demand): pressure should not drop more than 1" WC below static
Significant pressure drop under load indicates undersized gas line or regulator issues upstream.
Reset procedure
After addressing cause, cycle power to reset code 12. Most Richmond units allow 3 ignition attempts before extended lockout — if you've reset multiple times without addressing the underlying cause, the unit may require longer reset interval (typically 60 minutes) before retrying.
When to call a pro
Gas pressure measurement, igniter replacement on power-vent units, or any code 12 that recurs after standard diagnostic steps. Authorized Richmond service technicians have manometers and ignition module testers that confirm or rule out specific failure modes.