HVACopediaNavien · Combi boiler troubleshooting
Hot water not hot enough or too hot - Navien NCB-H
What is going on
DHW temperature at the taps is lower or higher than wanted.
Likely causes
- DHW set temperature too low or too high
- Cross piping between heating supply and return lines
- Flow above the unit's capacity for the temperature rise
Check in this order
- Check the DHW set temperature (range 86-140°F, default 122°F).
- Warning: water above 120°F can scald instantly.
- Water too cool? Look for a cross-connection between the heating supply and return piping.
- Compare the flow with the rated DHW flow at the needed temperature rise for the model.
Applies to: Navien NCB-H combi boilers: NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H
More combi boiler guides
Take it to the job
All guides, error codes and tips work offline in the HVACopedia app.
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.