Plumbing
What code 11 actually is
A Rinnai tankless heater lights by opening the gas valve, sparking the igniter, and then confirming the flame through a flame rod. Code 11 means that sequence ran and the flame was never confirmed. Either gas never arrived, the spark never happened, or the flame lit and the heater could not sense it.
That last possibility is the one that catches people out. The burner can visibly be alight while the heater reports code 11, because the fault is in sensing the flame rather than making it. Rinnai’s procedure has you look through the view window specifically to tell those apart.
The three checks worth doing yourself
- Confirm every gas valve in the run is open, at the heater, at the meter, and at the propane tank. This sounds too simple to be the answer and it regularly is, especially after other work in the house.
- If you are on propane, confirm there is gas in the tank and that the tank was sized for the load. A tankless heater draws hard, and a tank sized for a range will not hold pressure under one.
- Look at the intake and exhaust terminals outside. Snow, ice, a wasp nest, leaves, or painter’s tape left over a terminal will all do this. Rinnai calls out vent terminal clearance as a cause of incomplete combustion.
If none of those three is it, stop there. The next step in Rinnai’s own procedure involves unplugging the igniter lead and holding it with insulated pliers near the chassis while the unit cycles, which is a technician’s test, not a homeowner’s.
What a technician checks, and the numbers they check against
These are the figures from Rinnai’s service documentation. They are worth publishing because they are what separates a diagnosis from a parts swap, and because you are entitled to ask whether they were actually measured on your heater.
| What gets measured | Rinnai specification |
|---|---|
| Spark electrode gap | 0.138 in. / 3.5 mm |
| Spark electrode voltage, connector D, black pin 21 to red pin 12 | 11 to 13 VDC, and only during the ignition cycle |
| Inlet gas pressure drop, all appliances on high fire | No more than 0.3 in. W.C. on natural gas, 0.5 in. W.C. on propane |
| Maximum inlet gas pressure | 10 in. W.C. natural gas, 13.5 in. W.C. propane |
| Two-stage regulator distance from the heater inlet | At least six feet, with no bleed-through above maximum inlet pressure |
| Gas type parameter setting | Parameter 10 selection A for natural gas, B for propane |
From Rinnai Troubleshooting Tankless Water Heater Diagnostic Codes, document 100000652. Pressure drop limits are based on the National Fuel Gas Code, ANSI Z223.1 / NFPA 54.
Rinnai publishes the whole procedure, and it is public: Rinnai tankless diagnostic codes.
The floating flame rod
The finding that comes up most often is mechanical and unglamorous. The flame rod sits in a bracket with a gasket. If the gasket has failed and the rod is loose enough to move with a finger, Rinnai calls it a floating flame rod, and documents it as producing exactly this code. The same is true of a loose ceramic sparker electrode, which can drop far enough to touch the burners and short the spark out entirely.
The fix is to remove, clean and reinstall with a new gasket. Rinnai is explicit that the gasket must be replaced once the seal is broken, which is the step a hurried visit skips and the reason the code comes back.
Code 10 and code 12 are not the same fault
| Code | What it means | Where it usually comes from |
|---|---|---|
| Code 10 | Air supply or exhaust blockage | Build-up between the heat exchanger fins restricting airflow, or a vent problem. Rinnai notes that fin blockage leads specifically to a code 10. |
| Code 11 | No ignition | Gas supply, spark, or the flame rod never proving a flame that may or may not be alight. |
| Code 12 | Flame failure | The flame lit and then went out or stopped being sensed. Vent terminal clearances that let combustion gases recirculate are a documented cause. |
From Rinnai document 100000652. A loose flame rod can produce either 11 or 12.
Getting it sorted
We install and service tankless and tank water heaters on both fuels, and the licensed team covers the gas piping and the venting as well as the appliance, so nothing waits on a second contractor. Water heaters is the page, and gas line repair is the one if the real fault turns out to be supply rather than appliance.
A tankless heater that is descaled and had its burner and flame rod cleaned on schedule throws this code far less often. That is routine HVAC maintenance work. We cover Manchester and Dover in New Hampshire and Sparta and Brick in New Jersey.