HVACopediaRinnai · Tankless water heater troubleshooting
Checking PC board fuses and thermistors
What is going on
How the guide says to test the board fuses and the temperature sensors with a meter.
Likely causes
- Blown glass fuse on the PC board
- Thermistor open, shorted or out of range
Check in this order
- Disconnect power first, then pull each of the two glass fuses on the PC board and test continuity; no continuity means the fuse is blown and must be replaced.
- Unplug the thermistor connector and measure on the 20 k range at the thermistor side.
- Warm the sensor bulb resistance should fall. Cool it with ice: resistance should rise.
- Compare readings with the typical temperature/resistance table.
Applies to: SENSEI RX/CX (RX199i, RX180i, RX160i, RX130i, CX199i, CX160i, RXP199i, RXP160i, CXP199i, CXP160i)
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Source: Rinnai SENSEI RX/CX technical guide U362-0875, Electrical Diagnostics. 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.