HVACopediaNTI · Boiler troubleshooting
Excess flow valve (EFV) in the gas line
What is going on
Undersized EFV starves the boiler. Check its flow rating against the TRX150 input.
Likely causes
- EFV rated below the boiler gas demand, so it trips or chokes flow at high fire
- EFV rated above the boiler range, so it may not protect the line as intended
- Boiler runs rough or locks out only at high input, a typical sign of a restricted gas line
Check in this order
- Find the EFV rating on its label or the maker's sheet, because it is rated in flow, not in pipe size.
- Compare the min and max flow rating to the boiler input.
- If the rating is outside the range, replace the EFV. Gas work, so use a licensed gas fitter.
- After any gas work, leak check every joint you disturbed.
- Watch a full call for heat to confirm the boiler holds high fire.
Applies to: TRX150 gas line
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Source: NTI TRX150 manual, p. 55. 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.