HVACopediaRheem · Furnace troubleshooting
Burners go out before the heat call ends / short cycling
What is going on
Main burners do not stay lit until the thermostat is satisfied, or the room temperature is not held near setpoint.
Likely causes
- Pressure switch dropping out
- Limit opening (airflow, over-firing, rollout)
- Weak flame sense
- Thermostat location, anticipator setting, compatibility
- Oversized furnace
Check in this order
- Check whether the pressure switch drops out during the run (see 2 blinks).
- Check whether the limit circuit or the IDM wire through the aux. limit opens and closes - STATUS should show 3 blinks; check airflow, limits, rollouts and over-firing.
- Confirm the FLAME LED is steady on with burners lit; if blinking or off, clean the flame sensor and check ground/polarity.
- Make sure the thermostat is not affected by registers, fans, sunlight, heat through walls, pipes or wires in walls.
- Check the heat anticipator setting; the furnace may need an isolation relay (SPST, 24 VAC coil, contacts rated 0.5 A min at 24 V).
- Verify the furnace is correctly sized.
Applies to: Rheem (-)GRC/(-)GTC and 90RJ/90TJ 90 Plus condensing gas furnaces
More furnace guides
Take it to the job
All guides, error codes and tips work offline in the HVACopedia app.
Source: Rheem (-)GRC/(-)GTC Installation Instructions 92-24161-88-00, Figure 56 IFC Troubleshooting Guide, p.54 (printed); Rheem 90RJ/90TJ Installation Instructions 92-24161-32-08, Figure 53, p.54. Written in our own words; check the manual for your exact model.
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.