HVACopediaAllied · Furnace troubleshooting
Checking gas flow rate (approximate)
What is going on
Clocking the meter. Quick way to check actual gas input. Run furnace 5 min first so it is steady. Only this appliance on the meter. Compare against the Gas Meter Clocking Chart for the unit size and fuel.
Likely causes
- Orifices wrong size or partly blocked
- Manifold pressure off
- Other gas appliances left running during the test
- Meter dial misread
Check in this order
- Shut off all other gas appliances on the meter, including pilots.
- Time two revolutions of the meter dial in seconds.
- Divide that time by two to get the time for one revolution.
- Compare the result with the Gas Meter Clocking Chart for the unit size and fuel.
- If manifold pressure is correct and the flow rate is wrong, check the burner orifices for proper size and restriction.
- Remove any temporary gas meter that was installed.
- Relight other appliances after the test and leak-check any joint you disturbed.
Applies to: All sizes
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Source: Allied 92G1UH installation manual, p. 47. 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.