Noritz Error Code 66 is a specific diagnostic signal indicating a Bypass Valve Error. This means the electronic motor responsible for modulating the water flow between the heat exchanger and the bypass loop is either stuck, disconnected, or has suffered a mechanical failure, preventing the unit from accurately controlling the output water temperature.
đź“– Warning: Check Manual First
Don’t guess the wiring. Get the official PDF to see the exact schematics.
Listen, if you’re seeing this code, you’re likely dealing with a “cold water sandwich”—where your shower goes from hot to freezing and back again—or the unit might just quit on you entirely to prevent scalding. You might also hear a faint clicking or grinding sound coming from inside the cabinet as the valve tries (and fails) to find its home position. Don’t panic; I’ve dealt with this a thousand times. It’s usually a hardware hiccup that we can diagnose with a little patience and the right approach. It doesn’t necessarily mean your whole heater is toast.
- Difficulty: Intermediate – Requires opening the unit and basic electrical testing.
- Estimated Time: 45 to 90 minutes.
- Tools Needed:
- #2 Phillips head screwdriver (magnetic tip is a lifesaver here).
- Digital Multimeter (to check for voltage and continuity).
- Needle-nose pliers (for stubborn wire connectors).
- Estimated Cost: $0 (if it’s just a loose wire) to $180–$260 (if the bypass valve assembly needs replacement).
Common Symptoms of Error 66
In my experience, Error 66 doesn’t always just shut the machine down immediately; it often whispers its problems before it screams them. Here is what you should be looking for:
- The “Flashing 66”: This is the most obvious sign. The digital controller on the front of the unit or the remote will flash the code, often accompanied by an audible beep.
- Temperature Fluctuations: This is the hallmark symptom. Since the bypass valve isn’t mixing the water correctly, you’ll get bursts of scalding water followed by lukewarm or cold water because the unit can’t stabilize the flow.
- Abnormal Mechanical Noises: If you stand near the unit when it calls for hot water, you might hear a “hunting” sound—a rhythmic clicking or whirring. That’s the stepper motor inside the valve struggling to turn against a jam.
- System Lockout: Eventually, for safety reasons, the Noritz PC board will decide it can’t safely regulate the temp and will lock the unit out, leaving you with no hot water at all.
What Triggers this Code?
As a mechanic, I look at the “why” before I look at the “how.” The bypass valve is a precision instrument, and three main culprits usually take it down:
1. Scale and Mineral Buildup: This is the #1 killer. If you have hard water, calcium and magnesium deposits form inside the valve body. These deposits act like sand in a gearbox. The motor tries to turn the valve, hits resistance from the scale, and the PC board detects an over-current or a timing mismatch, triggering Error 66.
2. Stepper Motor Fatigue: Inside that valve is a small electric motor. Over years of constant “searching” to find the perfect temperature mix, the internal gears or the motor windings can simply wear out. It’s a mechanical part, and like any part with moving gears, it has a lifespan.
3. Wiring Corrosion or Connectivity Issues: Tankless heaters live in a world of heat and moisture. Over time, the molex connectors that link the bypass valve to the main PCB (Printed Circuit Board) can develop a thin layer of oxidation. If the signal isn’t 100% clean, the board thinks the valve has failed.
4. Voltage Spikes: Sometimes a local power surge can “scramble” the memory of the PC board regarding the valve’s position, or worse, fry the delicate control circuit that sends power to the valve motor.
The Complete Solution
The Complete Solution: Step-by-Step Fix
Follow these steps precisely. We’re going into the “gut” of the machine, so don’t take shortcuts.
Step 1: Power Down and Safety First
Before you touch a single screw, pull the power plug from the wall. If your unit is hardwired, flip the breaker. Never work on a live unit. Turn off the gas supply line as an extra precaution. Warning: High voltage components are exposed once the cover is off; ensure all power is disconnected.
Step 2: Remove the Front Cover
Use your Phillips screwdriver to remove the four screws (usually located at the corners) of the front panel. Pull the panel toward you and set it aside in a safe place where it won’t get stepped on. You are now looking at the heat exchanger, the fan, and the plumbing manifold.
Step 3: Locate the Bypass Valve
On most Noritz models, the bypass valve is located toward the bottom of the unit, usually on the right-hand side near the water outlet pipe. It’s a small plastic housing with a wire harness (usually 5 or 6 colored wires) leading back to the main control board. It looks like a small motor sitting on top of a pipe junction.
Step 4: Inspect and Reseat Connections
Trace the wires from the valve to the control board. Unplug the connector at the board and the valve (if applicable). Look for any signs of green corrosion or burnt pins. Use a can of electrical contact cleaner if you have it. Plug them back in firmly—sometimes a loose connection from unit vibration is all it takes to throw an Error 66.
Step 5: The Multimeter Test
Set your multimeter to Ohms (Resistance). You want to check the resistance of the motor windings. Refer to your specific Noritz model’s service manual for the exact Ohms (usually between 10 and 30 Ohms across specific wire pairs). If you see “OL” (Open Loop) or 0 Ohms, the motor inside the valve is dead and the whole valve assembly must be replaced.
Step 6: Replacing the Valve (If Necessary)
If the motor is dead, you’ll need to drain the unit. Close the cold water inlet and hot water outlet valves. Open the pressure relief valve to bleed the pressure. Unscrew the mounting screws holding the bypass valve in place. Be careful of the O-rings; they need to be seated perfectly on the new valve to prevent leaks. Swap the part, tighten the screws, and reconnect the wiring.
Step 7: Re-pressurize and Test
Turn the water back on slowly and check for leaks. Plug the unit back in. Turn on a high-demand hot water tap (like a bathtub). If the unit fires up and the code is gone, you’ve nailed it.
How to Prevent Error 66
I always tell my customers: “An ounce of prevention is worth a pound of expensive Noritz parts.” Here is how you keep that bypass valve from seizing up again:
- Annual Descaling: If you live in an area with hard water, you must flush your unit with food-grade white vinegar or a descaling solution once a year. This dissolves the calcium that jams the bypass valve and keeps the internal gears moving freely.
- Install a Scale Inhibitor: If you don’t want to buy a full water softener, at least install a “ScaleShield” or a similar polyphosphate filter on the cold water line leading into the heater. It keeps the minerals in suspension so they don’t stick to your valve.
- Use a High-Quality Surge Protector: These heaters have sensitive electronics. A simple $20 surge protector can save your $300 control board and your bypass valve from being “fried” during a summer thunderstorm.
FAQ
Frequently Asked Questions
Q: Can I just bypass the bypass valve to get hot water today?
A: No. The Noritz logic board is smarter than that. If it doesn’t receive the correct positional feedback from the valve’s sensor, it will lock out the ignition sequence as a safety measure. You need a functional valve to operate the unit safely.
Q: Is Error 66 covered under warranty?
A: Usually, yes, if your unit is under 5 years old (check your specific Noritz warranty). However, if the technician finds that the valve failed due to “scale accumulation” (lack of maintenance), Noritz may deny the claim. Keep your maintenance records!
Q: My unit is old; should I just replace the whole heater?
A: If your Noritz is over 12-15 years old and you’re seeing Error 66 along with other issues like a leaking heat exchanger, it might be time. But if the unit is otherwise clean, a $200 valve is much cheaper than a $3,000 new installation.