A Navien that flashes an error and goes cold usually has one of three problems: no gas reaching the burner, a clogged air filter, or scale choking the heat exchanger. The first two are quick checks. The third is a Pasadena specialty, because local water is hard. If a reset does not clear the code, or the heater is a decade old and failing repeatedly, the choice between repair and a new unit sits on our water heater replacement page. To have someone look at the heater, use the quote form.
What do the common Navien error codes mean?
Four codes cover most calls. E003 means the burner did not light, E012 means the flame lit and then went out, E004 means the unit senses a flame that should not be there, and E016 means the heat exchanger is overheating, often from scale. Codes vary by model, so confirm in your manual before acting.
A short table helps:
| Code | What it points to | What you can check |
|---|---|---|
| E003 | Ignition failure | Gas supply valve is open; other gas appliances work |
| E012 | Flame lost during run | Intake air filter, gas supply, vent connections |
| E004 | Flame sensed when none should be | Nothing safe to do: call for service |
| E016 | Heat exchanger overheated | Scale is likely; needs diagnosis and a flush |
| E030 | Exhaust temperature too high | Scale or combustion tuning; needs service |
| E110 | Exhaust blockage | Vent obstruction, filter, condensate; needs service |
Pressing reset over and over on a combustion code is the wrong response. A single trip can be a fluke, but a code that returns is the heater telling you something is wrong. Write down the code, the model number and when it appears, such as only on long showers.
Is it safe to try anything myself before calling?
A few checks are safe. Check the gas valve at the heater, confirm the power cord is plugged in, look for a clogged cold-water inlet filter, and clean the air intake filter if your manual says it is user-serviceable. Stop there. Do not open the front cover with power connected or touch gas or venting.
Smell gas near the heater and the answer is simple: walk out, call SoCalGas from the yard or street (1-800-427-2200), adding 911 if anyone is hurt or in danger, leaving every switch alone. A tankless unit burns gas inside a sealed system, and poor venting can push exhaust into living space. Changes to gas lines or vents are regulated work, so expect a permit and a plumber holding the proper California contractor license.
Why does a Navien struggle in Pasadena's hard water?
Because the heat exchanger is a narrow passage, and mineral scale narrows it further. Pasadena Water and Power's latest report puts hardness around 12 to 15 grains per gallon. Published Navien guidance, as summarized by service guides, treats water above roughly 12 grains as needing treatment such as a softener or a scale-prevention cartridge, and calls for an annual flush at lower levels.
Scale shows up as lukewarm output, long delays before hot water arrives, a rumbling or popping sound, and eventually E016 or E030. Navien states that damage from poor water quality is not covered under its warranty, so skipping the flush has a cost beyond the repair. If your unit is more than a year old and has never been flushed, a flush is the first thing to ask for. Our pages on hard water scale removal and water hardness by zip code explain the local picture, and a water softener system is the long-term fix.
What does a Navien service visit include?
A visit typically starts with reading the stored error codes and checking gas supply, venting, the condensate drain and inlet and outlet temperatures. The plumber then flushes the heat exchanger with a descaling solution and pump, cleans the filters, and tests combustion where the work calls for it. Ask for what was found written down.
Not every fault is scale. A failed igniter, flame rod, fan, sensor or control board needs parts, and parts are specific to the model number. Find out if the visit fee is credited when you go ahead, and request parts and labor itemized; the cheap plumber near me guide explains why.
Should I repair the Navien or replace it?
Repair when the unit is fairly new, the fault is scale or a single part, and the heat exchanger is sound. Replace when repairs repeat, the heat exchanger leaks, or the repair bill climbs toward the price of a replacement. A tankless unit that is flushed yearly can last well beyond the age at which a neglected one fails, but many guides do not give a single reliable figure.
Still weighing types? Tank versus tankless lists the trade-offs for a Pasadena house. Replacements need a permit in Pasadena, and the Permit Center handles simple plumbing permits over the counter; a plumber normally pulls it. Other brands have their own pages: Rinnai, Rheem and Noritz.
Common questions
Why does my Navien keep showing E003?
E003 is an ignition failure. The usual causes are a closed or low gas supply, a dirty or worn igniter and flame rod, or a blocked air or exhaust path. Look at the gas valve, then call if it is open. Repeated resets on an ignition code can wear parts, so avoid cycling the heater over and over.
How often should a Navien be flushed?
Navien's published water hardness guidance calls for a yearly flush across most hardness bands, with treatment recommended or required as hardness rises. Pasadena's water sits at the hard end, so plan on a yearly flush as the floor, and read your own model's manual. Keeping the receipt helps if a warranty question comes up.
Can I use vinegar to descale it myself?
A circulated descaling solution is the usual method, pumped around the heat exchanger through hoses, by someone with service valves to connect to. Doing it without service valves or in the wrong sequence risks damage and leaks. If the heater has no isolation valves, a plumber can add them during the visit.
Why is the water only lukewarm?
Common causes are scale, a clogged inlet filter, low flow through a worn fixture, or a mixing fault elsewhere in the house plumbing. Run hot water at a second fixture to compare. If the heater is cold at every tap, it is more likely the unit; if one sink only, the cause is local to it.
Does a Navien need a permit when replaced?
Yes in Pasadena, as with other water heater replacements. The permit covers gas, venting, seismic anchoring and energy requirements, and an inspection finishes it. The plumber you hire usually arranges it. Ask the Permit Center on (626) 744-4200 if you want to confirm what the city requires for your address.
For our other services, see the Pasadena Pipe Works home page.
Sources
- Navien error code and hard water flush guidance as summarized by independent water heater service guides, checked November 2026
- Navien, support and water treatment products
- Pasadena Water and Power, water quality FAQs
- City of Pasadena Permit Center, apply for a permit
- SoCalGas, natural gas leaks
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