Rinnai 65: Water Flow Control Fault

This one is specific to Rinnai units with a bath-fill feature: code 65 means the internal valve that's supposed to shut off water flow during an automated bath fill didn't close when it should have.

Applies to: Rinnai tankless water heaters with a bath-fill/water flow control feature.

What it means

Water Flow Control Fault — the internal water flow control valve failed to close during a bath-fill cycle. Because this valve controls water delivery during an automated fill cycle, a stuck-open fault isn't just an inconvenience — it can mean water keeps flowing when the cycle should have stopped.

Most common causes

There's really one documented cause here:

• Malfunctioning internal water flow control valve

What you can safely check yourself

Rinnai's own guidance for this code is unusually direct:

1. Rinnai's own guidance is to immediately turn off the water and stop the bath-fill function if you see this code — this is not a homeowner repair

What the fix costs

Because Rinnai itself doesn't publish this as a homeowner-serviceable fault, expect a standard diagnostic visit — $150–$600, per Angi and Fixr repair cost guides — plus the cost of the valve if it needs replacing. There isn't a published national parts price specific to this valve, so the most reliable next step is a quote from a licensed contractor rather than guessing at a number.

Related codes

• Rinnai 32 — Water Temperature Sensor Fault
• Rinnai 25 — Condensate Trap Error
• Symptom: water not hot enough or runs lukewarm

All Rinnai codes

Every Rinnai water heater fault code — the full list on one page.

Sources

• Rinnai bath-fill and water flow control feature documentation, owner's manual (manufacturer)