HVACopediaNavien · Boiler troubleshooting
Relief valve discharging - Navien NHB-H / NFB-H
What is going on
The pressure relief valve drips or discharges, or pressure climbs high when the boiler heats.
Likely causes
- Expansion tank waterlogged, undersized or isolated
- Make-up / pressure reducing valve over-filling
- Relief valve rating too low for the system pressure (NFB-H)
Check in this order
- Do not plug or cap the relief valve.
- Watch system pressure as the boiler heats; a large rise points to the expansion tank.
- Check the expansion tank pre-charge and size, and that it is on the pump suction side and cannot be isolated.
- Check the make-up water valve is not raising pressure above the fill setting (typical 12 psi).
- NHB-H system 12-30 psi with a 30 psi valve. NFB-H: 12-80 psi; if a higher-rated ASME valve (up to 80 psi) is fitted, set parameter 17 High Sys Pressure to suit.
- Replace the relief valve if it leaks after pressure is correct.
Applies to: Navien NHB-H and NFB-H condensing boilers
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Source: Navien NHB-H Installation and Operation Manual, 3.1.2 p.17-19 and 3.5 p.28; NFB-H Installation Manual 3.1.2 p.19-21, 11.6.3 p.109; NHB-H User's Information Manual p.20. 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.