16 Critical Moderate DIY

Rinnai Tankless Water Heater 16 — Outgoing Water Over-Temperature

Rinnai Tankless Water Heater · Error code 16

What 16 Means

Outlet water temperature exceeded the safety limit. Unit shuts down to prevent scalding and exchanger damage.

Symptoms

  • Hot water briefly very hot then cold
  • Code 16 after high-demand draw
  • Scale visible at fixtures

Common Causes

1
Scale in heat exchanger

Insulating scale layer causes localized superheat.

2
Low water flow

Clogged filter or partly closed valve — heat per unit volume is too high.

3
Faulty outlet thermistor

Sensor reading high or unstable.

4
Gas valve stuck open / over-firing

Modulating valve failing to throttle.

5
Recirculation crossover

Hot/cold crossover causing temperature creep.

How to Fix It

  1. Clean the inlet water filter and confirm full flow.
  2. Descale the heat exchanger with manufacturer-approved solution.
  3. Test outlet thermistor resistance per service manual.
  4. Check for hot/cold crossover at single-handle faucets and the recirc loop check valve.
  5. Verify gas valve modulates — if stuck, replace valve assembly.
  6. Replace outlet thermistor if out of spec.

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.

Common replacement Outlet thermistor View on Amazon→ Common replacement Descaling kit View on Amazon→

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 →

Verified against manufacturer documentation: rinnai.us

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.