Gas heating lockout. The control will not auto-reset. The chart says to check for a mis-wired gas valve or a defective control valve relay.
Bryant 21 on the 80% two-stage chart is a gas-heating lockout that will not auto-reset. The chart lists a mis-wired gas valve and a defective control valve relay. It is not code 22, which is flame proved while the gas valve is off. Code 21 does not clear on the 3-hour timer used by codes 13, 14, and 15.
Likely causes
- Mis-wired gas valve
- Defective control valve relay
Safe checks for 21
- Count 2 short flashes and 1 long flash. This lockout does not clear itself after 3 hours
- If you smell gas, leave the building and call the gas supplier from outside
- Techniciancheck the gas-valve wiring and the valve relay on the control
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician. Do not jumper the gas valve to get heat back.
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Parts & tools for this fix
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Furnace control board and low-voltage fuse: guide
In this code: Parts list for this code: Furnace control board
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