HVACopediaRheem · Furnace · Ignition
Gas heat call, direct spark ignition and retry
What happens, in order
- Thermostat contacts close and the inducer starts pre-purge
- Air proving pressure switch closes
- 30 s after the switch closes the spark igniter energizes; inducer runs all through the heat cycle
- Gas valve opens for the 8 s trial for ignition
- Flame sensor must prove flame for 1 s
- Main blower starts 20 s after burners light
- If the burners do not light valve closes, igniter off, 10 s post-purge, control checks the pressure switch reopened
- Next try 30 s pre-purge, igniter on and valve opens
- After the second miss the blower and inducer run together for 3 minutes before the next attempt
- Up to 4 attempts, then a 1 hour soft lockout; reset by cutting power for 5 to 10 s or by dropping and re-making the call for heat
Timings and thresholds
| Item | Value |
|---|---|
| Pre-purge | 30 s |
| Trial for ignition | 8 s |
| Blower on delay | 20 s after ignition |
| Post-purge | 10 s |
| Self-healing blower/inducer run | 3 min |
| Ignition attempts | 4 |
| Lockout | 1 hour |
Applies to: Rheem 90RJ series (direct spark control)
Models
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Related
Rheem error codes · Rheem tips · Rheem parts · All Rheem sequences
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Source: Rheem 90RJ installation manual, Sequence of Operation (UT electronic controls, direct spark ignition). Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.