Ignition proving failure. The control tries three more times before lockout 14. If the flame signal is lost during the blower on-delay, the blower runs the selected off-delay.
Homeowner part this code names: furnace flame sensor.
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Bryant 34 on the 80% two-stage chart is an ignition proving failure. The control tries three more times, then stores lockout 14. The chart lists low inlet gas pressure, ground continuity, a gas valve that is off or defective, a closed manual valve, oxide on the flame sensor, flame current of 0.5 microamps DC minimum with 4.0 to 6.0 nominal, the green/yellow wire on the furnace sheet metal, poor flame carryover, and a grounded flame sensor. It does not list a hot-surface igniter. Bryant 14 already on this site is the 926TB lockout, which also says to see code 34.
Likely causes
- Low inlet gas pressure
- Gas valve defective, turned off, or the manual valve shut off
- Oxide buildup on the flame sensor
- Control ground continuity problem, or the flame sensor is grounded
- Inadequate flame carryover or rough ignition
Safe checks for 34
- Check that the manual gas shutoff is open and the switch on the gas valve is ON
- Technicianclean oxide off the flame sensor with fine steel wool, and read flame current. This chart says 0.5 microamps DC minimum, with 4.0 to 6.0 nominal
- Technicianthe green/yellow ground wire must be connected to the furnace sheet metal
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician if the gas valve is on and 34 still goes to lockout 14. Bryant 14 on this site is the 926TB lockout. This 34 page is the 80% chart's own proving-failure list.
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Parts & tools for this fix
Taken from this code's causes or steps. A search link opens Amazon results and does not confirm a fit. Check the model number in the manual.
Furnace flame sensor: guide
In this code: Oxide buildup on the flame sensor
Nut driver set: guide
In this code: Panels and parts on a furnace are held by hex-head screws; a nut driver grips them without stripping.
See the guide for what to look for when buying one.
Multimeter for appliance and HVAC diagnosis: guide
In this code: Control ground continuity problem, or the flame sensor is grounded
This one is for a technician to test or replace, so we only explain it and do not link to buy it.
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