Rinnai In Use Light Not On: No Call for Heat
On this page (4 sections)
The Short Answer: On a Rinnai controller, the In Use indicator shows that hot water is being supplied. If it stays off when you open a hot tap, the heater is off, has no power, or has not detected enough flow to start. Check that the controller is on, open a high-flow hot tap, confirm the service valves are open, and clean the inlet water filter.
What a dark In Use light rules in and out
The heater only starts a heating cycle after its flow sensor detects water moving. A dark In Use light with cold water usually means it never got that far, so the problem is power, the controller, or flow rather than the burner. If the light is on and the water is still cold, the heater is trying to fire; look for a code and see Rinnai with no hot water.
Owner checks, in order
- Is the display on? A blank controller means no power to the heater or a controller problem. See Rinnai control panel not working.
- Is the heater switched on? Press On/Off. After a power interruption, check that it came back on.
- Open a high-flow hot tap, such as a bathtub spout, fully to hot. If In Use lights there but not at a bathroom sink or low-flow shower, the heater works and that fixture’s flow is below the activation point. Rinnai lists 0.4 gallons per minute as the minimum activation flow for its RSC models; other models are similar but check yours.
- Service valves. The hot and cold valves under the heater should be fully open, especially after a recent flush.
- Inlet water filter. Rinnai’s owner manuals describe cleaning the filter at the cold inlet: close the service valves, catch the water in a bucket, unscrew and rinse the filter, reinstall, and reopen the valves. A screen packed with sediment can stop the heater from seeing flow.
Problems a technician solves
Rinnai’s troubleshooting for “nothing happens when water flow is activated” includes items an owner cannot test:
- A water flow sensor or turbine that is stuck or has failed
- Hot and cold lines reversed on a new installation
- A crossover elsewhere in the plumbing (a failed mixing valve, for example) letting water bypass the heater; Rinnai’s V53De data sheet (opens in a new tab) calls this “bleed over”
- A controller that has power at its terminals but does not light
A flow sensor or controller is a part repair. A crossover is fixed in the house plumbing, not the heater.
Also see tankless with no water flow if hot water barely trickles from every tap.
Frequently Asked Questions
Q: My In Use light works at the tub but not the shower. Is the heater failing? A: No. The heater is working; the shower is not drawing enough hot water to start it. A low-flow head, a thermostatic valve mixing in lots of cold, or a clogged head or cartridge can cause it. Lowering the heater’s temperature setting so the shower uses more hot water can also help.
Q: Some controllers say Priority instead. Is that the same light? A: No. The Priority light shows which controller is allowed to set the temperature when there are several. The In Use indicator shows hot water is being supplied.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Rinnai: V53De technical data sheet (100000564), controller and No Code section (opens in a new tab)Rinnai V53De controller and no-code troubleshooting; other Rinnai models use similar controllers.
- Rinnai: RSC SENSEI installation and operation manual (100000773) (opens in a new tab)Rinnai RSC SENSEI minimum activation flow and inlet water filter maintenance.
- Rinnai: official document library (opens in a new tab)Select your exact model and owner manual before interpreting a fault or reset procedure.
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