71 Gas solenoid valve fault (SV0–SV4 on Non-SENSEI)

What the control is telling you

Fault in the gas solenoid valve circuit. On Non-SENSEI units it refers to a fault in solenoid valves SV0, SV1, SV2 or SV3.

Applies to: SENSEI Series, SENSEI RX/CX Series, Non-SENSEI Series

Likely causes

• Single PC board DIP switch not set to OFF (SENSEI / SENSEI RX/CX)
• Loose, broken or damaged solenoid valve wiring
• Grounded heater circuit
• Moisture in gas valve tubing from a leaking heat exchanger or vent condensate
• Open solenoid coil or mechanical obstruction in the gas valve
• Faulty PC board

Test and repair steps

1. SENSEI / SENSEI RX/CX Confirm the single DIP switch on the PC board is OFF.
2. SENSEI / SENSEI RX/CX Inspect the gas solenoid valve harnesses back to the PC board for loose, broken or damaged connections.
3. WARNING (all series) Turn off the electrical, gas and water supply to the heater before measuring or replacing parts.
4. SENSEI Connector D black #27–yellow #29 = 18 ~ 22 ohms or 11 ~ 13 VDC. SENSEI RX/CX: Connector CN9 black #3–yellow #4 = 11 ~ 13 VDC.
5. SENSEI / SENSEI RX/CX Make sure the heater circuit is not grounded, then replace the gas valve.
6. SENSEI / SENSEI RX/CX Replace the PC board; transfer data with the supplied cable or program manually per PCB Replacement Instructions (100000553 SENSEI, 100000854 RX/CX).
7. Non-SENSEI Inspect the harnesses to SV0, SV1, SV2, SV3 and SV4 back to the PC board for loose, broken or damaged connections.
8. Non-SENSEI Check the plastic tube from the bottom of the combustion box to the gas valve for moisture. If wet, replace the gas valve and pull manifold/burner to find the source.
9. Non-SENSEI If the heat exchanger leaks, replace it and any parts it damaged; if vent condensate drains back into the unit, add a condensate drain line at the top of the heater.
10. Non-SENSEI Check voltage at SV0 and SV1 while the unit tries to fire; if correct but the code persists, continue.
11. Non-SENSEI Measure SV0–SV4 resistance (values in the tech data sheet under the front cover). If any coil is open, replace the gas valve and burner manifold with new solenoids.
12. Non-SENSEI If 71 remains, replace the gas control valve; good coil readings do not rule out a mechanical obstruction inside it.
13. Non-SENSEI Replace the PC board.

Settings for these units

• RSC supply connection sizes · SENSEI
• RSC water quality limits · SENSEI
• RSC clearances to combustibles · SENSEI
• RSC temperature settings available · SENSEI
• RX supply connection sizes · SENSEI RX/CX
• RX water quality limits · SENSEI RX/CX
• RX water treatment and flushing by hardness · SENSEI RX/CX
• RX clearances to combustibles · SENSEI RX/CX