Rinnai Tankless With No Hot Water
The Short Answer: A Rinnai with no hot water is four folders: no 120 V, no call (flow/controller), a lockout code, or gas/ignition. Photograph the display. Watch the In Use light. Do not descale a dark controller. Lukewarm is a different page. Codes 10/12/17/25 have their own articles — use those once you have the digit.
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Search Intent & The Real Problem
Every fixture is cold. Not slow. Not lukewarm. Cold. This is the splitter. Lukewarm: not getting hot enough. Wait then hot: takes too long. Hot then dies: goes cold after a few minutes. In Use dark: In Use light not on. No water moving: no water flow. R53-class chassis: R53 problems.
What other guides get wrong
They start with a vinegar flush. Flushing a unit that never fires does nothing except flood a mixer. They paste every error code into one blob so you sand a flame rod on a 25. They tell you to turn it to 140°F. A dead Rinnai does not care about setpoint.
Step-by-Step Troubleshooting
Step 1: Display, In Use, and the exact cold
| What you have | Folder | Next |
|---|---|---|
| Blank display | Power / GFCI / PCB | Step 2 |
| Display Off, no In Use | Controller / remote | Turn On |
| In Use dark, display On | No flow call | Screen, valves, min GPM |
| In Use on, no flame, code | Lockout | Photograph; use that code |
| In Use on, flame, still cold | Mixing valve / crossover | Thermometer |
| After a storm or freeze | Outage / rain / split | After outage, after rain |
- What to look for: Closest hot faucet as the test, not the master shower 60 feet away.
- Required tools: Phone photo of the controller before you cycle power.
Step 2: 120 V — GFCI, disconnect, both the unit and the remote
- What to look for: Outdoor GFCI popped. Disconnect off. House breaker off. Remote cable unplugged so the pad is dead while the PCB still has power. Reset a GFCI once. If it trips again, leave it off.
- Required tools: Eyes, receptacle tester. A breaker that will not reset is a short — do not hold it On.
Step 3: Call for heat — valves, screen, activation flow
- What to look for: Isolation handles not parallel to the pipe. Cold-inlet screen packed. Fixture mixing below ~0.4–0.6 GPM. Recirc crossover. Open a tub spout. If In Use never lights, stay on the In Use path — do not start on gas.
- Required tools: Filter service, bucket.
Step 4: Read the code — then go to that page
| Code | Meaning | Article |
|---|---|---|
| 10 | Air / exhaust / full trap | Code 10 |
| 11 | No ignition | Gas cock, igniter — licensed if it repeats |
| 12 | Flame lost after light | Code 12 |
| 14 / 16 | Overheat / outlet too hot | Scale, low flow |
| 17 | Venturi blockage (SENSEI) | Code 17 |
| 25 | Condensate drain / pump | Code 25 |
| LC / 00 | Scale warning | Flush with service valves |
- What to look for: One power cycle after the obvious cause (cap, hose, GFCI, cock parallel). Same digit on the next shower is the end of DIY.
- Required tools: Jacket sticker. No manometer. NG ~3.5–7 in. w.c. / LP ~10–11 in. w.c. is licensed — confirm the plate. Do not purge the line.
Step 5: Flame on, water still cold — not the burner
- What to look for: 120°F at the Rinnai outlet, 100°F at the fixture = mixing valve or crossover. Dip-tube thinking does not apply to tankless; a failed mixer or a shower cartridge dumping cold into hot will. Gas on, fan on, water never rises: scale-insulated exchanger or a failed bypass (some models) — licensed flush or parts.
- Required tools: Contact thermometer at the outlet vs the faucet.
Do not set 140°F to chase a mixer.
When DIY Ends: Calling a Licensed Pro
You may restore one GFCI, turn the controller On, rinse the inlet screen, open isolation valves, photograph a code, and power-cycle once. Stop at gas odor, a wet cabinet, a silent fan, a freeze-split, a repeating 10/11/12, and any jumper. Combustion, gas pressure, flame rod, PCB, and exchanger work are licensed. A cold Rinnai with a packed screen is a rinse. A cold Rinnai with a 12 that returns is a service truck.
Frequently Asked Questions
Q: Why does my Rinnai tankless have no hot water? A: No 120 V, controller Off, flow below activation, a lockout code (10/11/12/14/16/17/25), or a mixing valve hiding a hot outlet. Photograph the display and watch In Use before you buy parts.
Q: How do I reset a Rinnai with no hot water? A: Photograph the code, fix the obvious cause, power off 10–30 seconds. One try. A code that returns is licensed. Do not reset a wet cabinet or a unit that smells like gas.
Q: Should I flush a Rinnai that will not heat at all? A: Not first. Flushing treats scale on a unit that fires. A dark controller, a 10, or a 25 needs power, vent, or drain — not acid.