Rinnai · Tankless Water Heater Serious

51 — Gas Solenoid Valve Fault

Open or short detected in the gas valve solenoid circuit, or the valve isn't responding correctly.

Keep using it?
Limited use only
DIY difficulty
Hard
Verified against
rinnai.us ↗

How to fix it

  1. Power down and lock out gas.
  2. Inspect gas valve solenoid harness for damage; reseat connector.
  3. Measure solenoid coil resistance per service spec.
  4. Replace gas valve assembly if coil is open/shorted.
  5. If valve and wiring test good, replace the PCB.

Why it happens

Typical signs: Code 51 on ignition attempt · No burner operation · Click without ignition

  • Failed gas solenoid coil Open winding.
  • Wiring open or shorted Harness from PCB to gas valve damaged.
  • Loose connector Backed off the solenoid terminal.
  • PCB driver failure Board can't actuate solenoid.

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

  • Gas valve assembly Common replacement
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More Rinnai tankless water heater codes

02 02 — Power Interruption / Memory Loss 03 03 — Loss of Communication / EZConnect Issue 10 10 — Air Supply or Exhaust Blockage 11 11 — No Ignition 12 12 — Flame Failure 14 14 — Thermal Fuse / Overheat Cutoff

All Rinnai codes → All tankless water heater codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: rinnai.us.