HVACopediaNavien · Combi boiler troubleshooting
Hot water is cold or turns cold - Navien NCB-H
What is going on
Water at the tap stays cold or goes cold during a draw.
Likely causes
- Draw below the 0.5 GPM needed to start DHW
- Active error code
- Clogged inlet filter
Check in this order
- Open the tap wider - the boiler needs at least 0.5 GPM to detect a DHW demand.
- Check the front panel for an error code and look it up.
- Clean the DHW cold inlet filter.
- Check Status Information > 15. DHW Flow while the tap is open.
Applies to: Navien NCB-H combi boilers: NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H
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Source: Navien NCB-H User's Information Manual Version 1.0 (April 2024), 5.1 Solving Basic Problems, p.24. 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.