What does Rinnai error code 16 mean?

Rinnai titles code 16 High Outgoing Water Temperature, with the note that it is a safety shutdown because the outlet water temperature exceeded 203 degrees Fahrenheit (95 degrees Celsius). Rinnai's diagnostic manual says it applies to both the SENSEI series and the older non-SENSEI models.

To put that number in context, Rinnai's installation and operation manual for a SENSEI model gives a controller range with a top setting of 140 degrees Fahrenheit. The factory maximum is 120 degrees, and 140 is reachable only through a parameter adjustment. A trip point of 203 degrees is far past anything a person would dial in. So code 16 does not mean the temperature was set too high. It means the heater failed to hold the temperature it was told to hold, and a backstop ended the run.

### Is code 16 the same as code 14?

No, and the difference is worth knowing when you talk to a technician. Code 14 is an overheat device on the heat exchanger itself, a resettable bi-metal switch or a one time thermal fuse. Code 16 is about the temperature of the water leaving the heater. Both are heat safeties, but they are different sensors reporting different conditions. Our page on Rinnai error code 14 covers the heat exchanger version.

The diagnostic manual lists eight steps, in this order:

1. 1Check for restrictions in the air flow around the vent terminal.
2. 2Check the fan for proper operation.
3. 3Verify that the check valve behind the fan motor is not stuck in a way that restricts air flow.
4. 4Check for foreign material in the combustion chamber and the exhaust piping.
5. 5Check for a blockage in the heat exchanger.
6. 6Verify the water heater is set for the right gas type, using the rating plate on the side of the heater. On a SENSEI model, verify that parameter 10 was selected correctly, where A is natural gas and B is propane.
7. 7Replace the gas valve assembly.
8. 8Replace the fan motor assembly.

Notice the pattern. The first six items are about air and fuel. A heater that gets too much gas for the air it is moving will heat past its target, and a heater with the wrong gas type set will do the same. The last two are parts replacements, and Rinnai's owner-facing section of the same manual boils the whole code down to two lines: confirm the fan motor is working correctly and replace the gas valve assembly if it is not resolved.

The manual does not publish a reset procedure for code 16. That matters, because it means you should not expect to clear this one by cycling power and carrying on. Rinnai's own list starts with finding out why the heater ran hot.

Very little, and that is on purpose. A heater that overheated has been through a condition its safeties were built to stop, and Rinnai's manual says only trained and qualified professionals should follow its service instructions.

Gas smell first. If you smell gas at any point, do not try to light or reset anything, do not touch a switch, and do not use a phone inside. Leave and call Southwest Gas at 877-860-6020, or 911. Rinnai's manual says the same and adds to look for the smell next to the floor, since some gas settles low.

With no smell, three things are reasonable:

• Look at the vent terminal outside, where you can see it from the ground. Rinnai's first step is a restriction in the air flow around it. If something is stacked against it or covering it, that is worth telling the technician, and clearing it is fine if the heater is off and you can do it from the ground.
• Check the water at the tap with your hand or a thermometer, carefully. Rinnai's manual warns that water over 125 degrees Fahrenheit can cause severe burns, and gives first degree burn times of 3 seconds at 140 degrees, 20 seconds at 130 degrees and 8 minutes at 120 degrees. Children and elderly people are at the highest risk. If the water is scalding, run cold first and keep everyone away from the tap.
• Note the controller setting and anything unusual. Did the water turn suddenly very hot before the code, or did it simply stop? Did anyone recently work on the gas or the vent? That history helps.

Do not open the cabinet, and do not change the parameter for the gas type. A wrong gas setting is one of the eight items on Rinnai's list, and it is the kind of thing that is corrected with the manual and the right pressure readings, not by trial and error.

### Should I keep the heater running until someone comes?

Leave it off. Rinnai treats 203 degrees as a safety line, and a heater that crossed it once has a reason. Turn off the hot water at the fixtures you use most, use cold water where you can and book the visit. A heater that is off cannot make the situation worse while you wait.

Item 5 on Rinnai's list, a blocked heat exchanger, is where local water comes in. Scale in a heat exchanger acts like insulation and creates hot spots. Rinnai's maintenance section says scale is caused by hard water and can be made worse by a high temperature setting, and it says the flush is the owner's responsibility. The City of Phoenix publishes its water quality reports each year, and the local supply is hard enough that scale is a routine maintenance topic here, so a heater that has never been flushed is a candidate. Our page on how often to descale a tankless water heater in Phoenix gives a schedule, and our page on the Rinnai LC scale code explains the warning Rinnai gives before scale reaches this point.

### What will the technician do?

Expect the visit to follow Rinnai's order. The technician looks at the vent and the intake first, because those are quick. Then the fan and the check valve behind it, the combustion chamber and the exhaust, and the heat exchanger fins. The gas type setting is confirmed against the rating plate. Only after those steps do the gas valve and fan motor become candidates for replacement. If you can tell the technician what you saw and heard before the code appeared, and how old the heater is, you shorten that process.

Call for any code 16, because Rinnai's steps run through the gas valve, the fan and the heat exchanger and there is no owner fix on the list. Call right away if the water at the tap is scalding, if the heater smells of burning, or if you smell gas.

HQ Plumbing and Air is licensed and insured, and our emergency line answers 24/7. Estimates are free and pricing is upfront before any work starts. For the rest of the codes, see the Rinnai tankless code list. If yours is a different brand with a similar high temperature shutdown, our pages on Takagi codes and Rheem tankless codes may help.