HVACopediaNoritz · Tankless water heater
MM49 Maintenance monitor 49 - fan speed
What the display is showing
Shows fan speed as a percentage. A healthy heater normally reads 100; a value above 100 points to a restriction in intake or exhaust. Read it with the front cover on, as in normal use. Used mainly for code 90.
Applies to: NRC/NRCP and older
What to do
- Open the maintenance monitor (display window, remote or EZ Start Plus app).
- Select the MM number.
- Read the value, compare with set temperature and expected behaviour.
Settings for these units
- Indoor clearances (required and recommended) · Noritz NRCR
- Operation panel menu settings and defaults · Noritz EZ, Noritz NRCR
- Water quality limits · Noritz EZ, Noritz NRCR
Models that show this code
6 models in Noritz NRC/NRCP
Other codes on the same units
- 66 Bypass water control servo abnormality
- 73 Circuit board setting abnormality
- 90 Combustion abnormality
- F76 Multi-system communication error
- MM14 Maintenance monitor 14 - flow rate
- MM30 Maintenance monitor 30 - inlet water temperature
- MM31 Maintenance monitor 31 - outlet water temperature
- MM32 Maintenance monitor 32 - heat exchanger water temperature
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Source: Noritz Residential Level 2 (NRC/NRCP and older, R2 V1), Maintenance Monitors, p.12, 15. Summarized in our own words; check the original manual for your 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.