Replacing Water Servo Valve on a Rinnai Non-Condensing Heater

Replacing a water servo valve on a Rinnai Non condensing tankless water heater is a critical repair task that ensures your unit efficiently regulates water flow and burner operation.

Why Replace the Water Servo Valve?

The water servo valve is like the “traffic controller” of your Rinnai heater. It uses a tiny water-powered turbine to tell the burner how much hot water to produce. If it fails, you’ll notice:

• No hot water when you open a faucet.
• Error codes 11 or 12 (ignition/flame failure) on the display.
• Strange silence from the heater (no fan or clicking sounds).

Tools & Supplies You’ll Need

1. Basic Tools:
   • Magnetic Phillips screwdriver (the magnet holds screws so they don’t drop into the heater).
   • Socket wrench (for #8 screws – common in Rinnai units).
2. Replacement Parts:
   • New water servo valve (matching the part number with your model is important).
   • O-rings (M10B-2-14 – often included with the valve).

Finding Your Model Number:

• Look for a white sticker on the left side of the heater. it has the model number and serial number.
• If missing, check the installation manual’s “exploded view” diagram (often stored in a plastic bag inside the front cover). In it there are troubleshooting guides along with exploded view of all the parts and their replacement part numbers. This is very useful, take a photo on phone and keep it.

Step-by-Step Removal of the Water Servo Valve

Step 1: Safety First – No Shortcuts!

1. Turn Off Power:
   • Internal units: Unplug from the wall.
   • External units: Flip the circuit breaker or switch labeled “water heater.”
   • Double-check: Use a multimeter set to voltage mode. Touch the terminals – if it reads 0V, you’re safe.
2. Shut Off Water:
   • Close the blue and red isolation valves below the heater.
   • Open a hot water faucet to drain leftover pressure.
3. Shut Off Gas supply: Close the Gas supply to your heater by rotating the gas valve.

Step 2: Remove front panel and PCB boards(if needed)

Remove front panel by removing two screws and releasing two latches. If your model has PCB boards in front of the servo valve remove them. Remove one screw securing PC Board to unit. Remove controller, PC board and pump PC board (pump models only) from their location and let them rest next to the water heater.

Step 3: Disconnect Wires – Label Everything!

1. Remove the Wire Harness Cover:
   • Find a white plastic clip which is used to bind the wires together near the servo valve, remove it to expose the wires individually.
2. Disconnect Wires One by One:
   • Aqua Blue Connector: Press the tiny tab on the connector and this wire goes to the bypass valve.
   • Maroon/red Connector: Follow this from the flow sensor to its plug connector – squeeze the sides to unclip it.
   • White connector: Check other connectors from the servo valve and unplug them.
   • Pro Tip: Take photos or label wires with tape to avoid confusion later.

Step 4: Remove the Heat Exchanger Pipes

1. Unscrew the Pipe Clamps:
   • Locate two screws securing the pipes coming from the heat exchanger to the servo valve. There are two pipes one from the cold water and another is a mix. If it an old unit screws might be rusty or jammed try to open them with screw driver and gently tap the screwdriver with a rubber mallet– If that is not working spray with penetrating oil (e.g., WD-40) and wait 5 minutes.
2. Wiggle the Pipes Free:
   • Hold the servo valve steady with one hand. Use your other hand to rock the pipes back and forth until they slide out from the Servo Valve.
   • Warning: Don’t bend the pipes – they’re fragile!

Step 5: Take Out the Old Water Servo Valve

1. 1. Remove the Water Inlet Valve:
      • Unscrew the two #8 screws on the inlet valve (located below the servo valve under the unit).
      • Pull the valve straight out – it might resist if old O-rings are stuck. If the O ring is damaged replace it with new one.
   2. Locate the Hidden Screw:
      • Underneath the unit, identify the last screw that holds the water servo valve. This screw is critical because it centers the valve when you install the new one.
      • Remove it with your socket wrench.
   3. Takeout the servo valve and detach the sensor:
      • Now take the Servo out from the unit from the gaps between the heat exchanger pipes by gently moving them side wards.
      • There will an another wire connected to the Servo assembly which is the sensor. find the ceramic sensor (looks like a white pill).
      • Unscrew its mounting screw, then slide the sensor out and keep it safe.
   4. Sensor 1:
      • There will an another wire connected to the Servo assembly from the unit which is the ceramic sensor (looks like a white pill).
      • Unscrew its mounting screw, then slide the sensor out and keep it safe.
   5. Sensor 2:
      • There is an another sensor beside the big ceramic sensor slot on the servo valve, remove the mounting screw it has a burgundy color wire connector.

Step 6: Removing Bypass Stop attached to Servo valve:

• Remove the bypass stop by unscrewing the two screws that secure it.
• Pull bypass stop and servo valves away to separate them.

Installing the New Water Servo Valve

Step 1. Prepare the Replacement Valve

• Match Parts:
  Ensure that the replacement water servo valve is the correct part for your specific model (refer to the service manual or parts list found in the front cover bag).
• Replace Washers and O-Rings:
  Use the new washers and O-rings that come with the replacement valve. These small parts are critical for preventing leaks.
• Attach the sensors which we removed from the old one:
  Attach the sensor 2 first which has wire with burgundy color connector which fits like a screw. Next mount the ceramic sensor in its slot and tighten it with a washer screw.

Step 2. Attach the Bypass stop with New Servo valve

Attach them with new O ring placed inside the New servo valve and tighten the 2 screws which we removed.

Step 3. Position the New Valve

• Alignment is Key:
  Place the servo assembly in the unit same as we took out. New water servo valve should align such that the white motor faces the back of the tankless heater, while the bypass valve sits towards the printed circuit board (PCB).
• Initial Screw Installation:
  Begin by installing the screw under the unit near the water inlet valve that centers the valve. Do not tighten it completely until all other components are aligned.

Step 4. Reattach the Heat Exchanger

• Reinstall the Heat Exchanger Pipes:
  Check all the O rings and carefully reinsert the heat exchanger pipes into the the servo valve assembly, if they resist, twist slightly while pushing. Tighten the screws along with the clamps.

Step5. Reconnect all the wires and connectors

• Reattach the blue, maroon, and white wire connectors to the water servo valve harness.
• Verify that the connectors click into place securely. The wiring should be routed so that it does not become trapped behind the valve.

Step6: Reinstall the Water Inlet Valve

• Secure the Water Inlet Valve:
  Reinstall the water inlet valve along with its union half and secure it using the original number eight screws.
• Ensure a Proper Seal:
  Check that the new o-rings are in place to prevent leaks when the water is turned back on.

Final Checks and System Restart

1. Turn the Water Supply Back On:
   • Carefully turn the water back on and inspect all connections for leaks.
2. Restore Power:
   • Reconnect the power supply or flip the switch back to the “on” position.
3. System Flush:
   • Open the hot water faucet to flush the system and ensure that everything is working properly. Listen for the familiar clicking of the relief valve and the operation of the water servo valve.
4. Check:
   • Open a hot water faucet. Within 10 seconds, you should hear:
     • A click (igniter).
     • A whoosh (burner firing).
     • Steady hot water!
5. Troubleshooting
   • Leaks at the Valve?: Tighten screws slightly or replace O-rings.
   • No Hot Water?: Check wire connections – a loose plug is the #1 issue.
   • Still Error Codes?: Call Rinnai support – your valve might need calibration.

Why Replacement Beats Cleaning

While cleaning the turbine (inside the valve) can sometimes work, hard water minerals or debris often permanently damage the tiny blades. A new valve ensures long-term reliability.

Tips for a Successful Repair

• Keep the Service Manual Handy:
  The small paper tucked inside the front cover contains exploded views of the unit’s components, error codes, wiring diagrams, and troubleshooting tips. Always refer to it during repair.
• Use the Right Tools:
  A magnetic screw tray and a proper socket set can make the process much smoother and prevent lost screws or clips.
• Be Patient with Old Units:
  Older units might have corroded or seized screws. In such cases, gentle taps or even drilling out a screw might be necessary—but proceed with caution.
• Safety is Paramount:
  Always ensure that the unit is completely powered down and that water connections are secure before beginning your work.

For more detailed guides, troubleshooting tips, and repairs, visit TanklessHelp.com and If you have any doubts please write down below.