Rinnai Tankless No Hot Water: Where to Start
On this page (4 sections)
The Short Answer: When a Rinnai gives no hot water anywhere, the controller tells you where to look. A blank display means power. A display with no In Use light means the heater is not detecting flow. An error code means the heater tried and stopped for a specific reason. Write down what you see, do the matching owner check, restart once, and call a technician if a code returns.
Read the display before touching anything
| What you see when a hot tap is open | Where the problem is | Next step |
|---|---|---|
| Display blank | No power, tripped GFCI, controller or board fault | Control panel not working |
| Display shows the heater is off | Controller off, often after an outage | Press On/Off |
| Display on, In Use not lit, no code | Flow not detected | In Use light not on |
| A number flashing | Fault code | See the code list below |
| Burner runs, water at the tap still cool | Mixing valve or crossover, or heater at capacity | Not getting hot enough |
Use the hot tap closest to the heater for this test. A distant shower adds pipe delay and mixing-valve variables.
Codes most often behind no hot water
These meanings come from Rinnai’s SENSEI manual (opens in a new tab); older models share most of them.
- 10 Air supply or exhaust blockage, or (SENSEI) condensate trap full: code 10
- 11 No ignition: gas valve closed, empty propane, air in a new gas line, or an ignition fault
- 12 Flame lost after lighting: code 12
- 14 Heat exchanger overheat or thermal fuse: code 14
- 17 Venturi blockage (SENSEI only)
- 25 Condensate pump or drain: code 25
- LC codes Scale buildup; the heater needs flushing (see how to flush a tankless water heater)
For code 11, the owner-level checks are the same as for any gas appliance: the gas valve to the heater is open, other gas appliances work, and a propane tank has fuel. Rinnai’s lists also include bleeding air from gas lines (see Rinnai code 11) and checking igniter and gas valves, which are technician tasks.
The order that saves time
- Check power: breaker, service switch, GFCI on outdoor units (reset once).
- Press On/Off if the controller shows off.
- Open a high-flow hot tap fully and watch for the In Use light.
- Note any code, fix the obvious cause the code points to, and restart once.
- If the same code returns, leave the heater off and book service. Give the technician the code and when it happened.
A heater that just went through a freeze, a flood, or a lightning storm is a special case. See Rinnai frozen and Rinnai after a power outage before restarting.
Frequently Asked Questions
Q: Should I flush my Rinnai if it gives no hot water? A: Not as a first step. Flushing removes scale from a heater that runs. If the heater never lights, is blank, or shows a vent or condensate code, flushing will not help.
Q: Hot water returned after a restart. Do I still need service? A: If a code caused it and you fixed an obvious cause (snow on the vent, a closed gas valve), probably not. If it happened without an explanation, write down the code; most Rinnai controllers keep a code history a technician can read if it happens again.
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: RSC SENSEI installation and operation manual (100000773), section 5.6 Diagnostic Codes (opens in a new tab)Code meanings for Rinnai RSC SENSEI models; non-SENSEI models share most codes but confirm in your manual.
- Rinnai: official document library (opens in a new tab)Select your exact model and owner manual before interpreting a fault or reset procedure.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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