Rheem 305, 505, 705 Error 14: Thermal Fuse

Tankless water heater · taken from the manufacturer’s manual, pages cited

Fault code14

Thermal Fuse indicates a problem with gas type mismatch or restricted airflow, possibly due to foreign materials in combustion chamber or exhaust piping. The manual's first action is: “Check for restrictions in air flow around unit and vent terminal.”

Model
Rheem 305, 505, 705
Display shows
Thermal Fuse (14)
Type
Fault code
Source
Manual p. 10

What 14 means

Thermal Fuse p. 10

Common causes

  • Check gas type of unit and ensure it matches gas type being used. p. 10
  • Check for low water flow in a circulating system causing short-cycling. p. 10
  • Check for foreign materials in combustion chamber and/or exhaust piping. p. 10
  • Check heat exchanger surface for hot spots which indicate blockage due to scale build-up. p. 10
  • Measure resistance of safety circuit. p. 10
  • Check for improper conversion of product. p. 10

What to do

  1. Check for restrictions in air flow around unit and vent terminal. p. 10
  2. Ensure dip switches are set to the proper position. p. 10
  3. Check heat exchanger surface for cracks and/or separations. p. 10
  4. Refer to instructions in manual for flushing heat exchanger. p. 10
  5. Ensure high fire and low fire manifold pressure is correct. p. 10

Before you service the product, read the safety instructions in the manual p. 4.

If 14 is still not resolved

  • Immediately call your gas supplier from a neighbor’s phone. p. 1
    “Immediately call your gas supp lier from a neighbor’s phone.”
  • If you cannot reach your gas supplier, call the fire department. p. 1
    “If you cannot reach your gas supplier, call the fire department.”
Open the manual at page 10 All 305, 505, 705 error codes Manual details & download

This page summarises what the manufacturer’s manual says about 14; each statement links to the page it comes from, and quoted lines are copied word for word. It is not a substitute for the manual or for a qualified installer. ManualLib is not affiliated with Rheem. Found a mistake? Report an error.