Rinnai Error Code 70 indicates a “PC Board Connection Fault” or a general failure of the unit’s main logic board. In plain English: the brain of your water heater has suffered a stroke. It can no longer communicate with the sensors, gas valves, or ignition system, leading to an immediate system lockout for safety.
🛠️ Safety First: Read Before Repairing
Before unscrewing any panel, ensure you have the correct service manual for safety.
Listen, I know there’s nothing worse than stepping into a shower and getting hit with a blast of ice water. You might hear the fan kick on, or perhaps a faint clicking, but then—silence. The digital controller starts flashing that dreaded “70.” Don’t panic yet. While the PC board is the most expensive part of the unit, it’s a straightforward swap, and in some cases, it’s just a loose connection caused by years of vibration. We’re going to get this sorted.
Quick Fix Specs
| Difficulty | Moderate / Intermediate |
| Estimated Time | 45 – 90 Minutes |
| Tools Needed | Phillips Head #2 Screwdriver, Digital Multimeter, Needle-nose Pliers, Anti-static Wrist Strap (Recommended) |
| Estimated Cost | $200 – $550 (Depending on model and warranty) |
Symptoms of a Failing PC Board
- The Flash of Doom: The digital controller or the front panel display pulses the number “70” repeatedly.
- No Ignition: You hear the combustion fan start up (the “whoosh” sound), but you never hear the “click-click-click” of the igniter or the roar of the flame.
- Lukewarm Water Surges: Before the board fails completely, it may provide intermittent hot water, followed by a sudden shutoff mid-shower.
- Unresponsive Interface: You try to change the temperature on the controller, but the buttons do nothing, or the display stays blank despite having power at the outlet.
- Strange Clicking: A rapid, erratic clicking sound coming from the internal relays on the board itself, even when water isn’t running.
Detailed Diagnosis: Root Causes
Detailed Diagnosis: Root Causes
When I crack open a Rinnai unit and see an Error 70, I’m looking for one of three culprits. You see, these boards are high-precision electronics living in a harsh environment of heat and vibration.
1. Voltage Spikes and Dirty Power: This is the number one killer. Tankless units are essentially computers that burn gas. If you had a lightning strike nearby or a surge from the local utility grid, it can fry the delicate capacitors or integrated circuits on the board. Unlike a fuse that just blows, a surge often “ghosts” a board, leaving it partially functional but unable to pass internal self-tests.
2. Moisture and Corrosion: If your venting isn’t pitched correctly or if there’s a tiny leak from the heat exchanger, moisture can drip onto the control box. Even a microscopic amount of mineral-rich water can bridge two solder points on the back of the board, causing a short circuit. I’ve seen boards where a single drop of condensation caused a permanent Error 70.
3. Thermal Cycling & Solder Fatigue: These units get hot, then cold, then hot again. Over 5 to 10 years, that expansion and contraction can cause “cold solder joints.” This is where the metal connection between a component and the board literally cracks. It might look fine to the naked eye, but the electrical path is broken, leading to a communication failure.
Comprehensive Repair Guide
Comprehensive Repair Guide
Step 1: The Hard Reset & Power Cycle
Before you go spending hundreds on parts, try the “Mechanic’s Reset.” Unplug the unit from the wall outlet. Wait exactly 60 seconds. This allows the capacitors on the board to fully discharge. Plug it back in. If the error clears and stays clear, it may have just been a temporary logic glitch. If it returns immediately, proceed to Step 2.
Step 2: Accessing the Interior
Use your Phillips head screwdriver to remove the four screws holding the front cover in place (usually two at the top and two at the bottom). Carefully pull the cover toward you. If your unit has a built-in controller on the front, be careful—there is a thin wire connecting the cover to the internals. Disconnect that wire clip before setting the cover aside.
Step 3: The “Jiggle” Test (Connection Check)
Locate the PC board—it’s usually housed in a plastic or metal box toward the bottom right. Look at the plastic wiring harnesses plugged into the board. Over time, vibration from the fan can loosen these. Press firmly on every single connector to ensure they are “seated” or clicked into place. Look for any loose white, red, or black wires that might have vibrated out of their terminals.
Step 4: Visual Inspection for Burn Marks
Smell the board. Does it smell like burnt plastic? Look for “blackened” areas or swollen capacitors (the little cylinders on the board). If you see any signs of scorching, the board is toast and must be replaced. Also, check the fuse—most Rinnai boards have one or two glass fuses. Use your multimeter to check for continuity. If the fuse is blown, replace it; if it blows again immediately, the board has a short.
Step 5: Board Replacement (The Heart Transplant)
If you’ve confirmed the board is dead, you’ll need the exact part number from your model’s manual. When the new board arrives, take a photo of the old board’s wiring. Disconnect the harnesses one by one. Unscrew the mounting screws. Install the new board, reconnect the wires exactly as they were, and—this is crucial—check the “Dip Switches.” You must set the tiny plastic switches on the new board to match the positions of the old board, as these control your altitude and gas type settings.
How to Prevent Error 70
Once you’ve fixed it, you don’t want to do it again in two years. Here is how you protect that new investment:
- Install a Dedicated Surge Protector: Don’t just plug the unit into the wall. Buy a high-quality single-outlet surge protector rated for appliances. This is the cheapest insurance you can buy against Error 70.
- Monitor for Leaks: Once a year, take the cover off and look for any white powdery residue (calcification) near the top of the unit. This indicates a small leak that could eventually drip onto your electronics.
- Ensure Proper Grounding: A “floating ground” in your home’s electrical system can wreak havoc on PC boards. Have an electrician ensure the outlet used for the water heater is properly grounded to the house’s main ground bus.
FAQ
Frequently Asked Questions
Q: Can I repair the individual components on the PC board myself?
A: I wouldn’t recommend it. While you might see a burst capacitor, these boards are multi-layered. Soldering on them without professional equipment can lead to a house fire or a gas leak if the safety logic is bypassed. Replace the whole board; it’s the only way to guarantee the unit is safe.
Q: Is Error 70 covered under Rinnai’s warranty?
A: Generally, yes. Rinnai usually offers a 5-year warranty on parts. However, they may deny the claim if the failure was caused by an “act of God” (lightning) or improper installation. It’s always worth calling their support line with your serial number ready.
Q: Why does the error go away when I reset it, but come back an hour later?
A: That’s a sign of a “failing” component, often a relay or a capacitor that fails once it reaches operating temperature. As the component gets hot, the electrical resistance changes, and the board’s self-diagnostic finally catches the error. It’s a sign that total failure is imminent.