Rinnai fault code 14
Thermal fuse activated (overtemp).
What 14 actually means
The thermal fuse has activated. Something got hot enough inside the unit to trip a one-shot safety device, and that device does not reset.
What causes it
- Blocked flue or exhaust path
- Fan failure so combustion products are not being cleared
- Heat exchanger scaled up internally, which is common on hard water
- Overheating from a water flow restriction
Most likely first. That order is from what we actually find on site, not from the manual.
Safe to check yourself
No tools, no covers off, nothing to do with gas, refrigerant or wiring.
- Turn the unit off at the power point and leave it off
- Do not attempt to reset it
What we check on site
So you know what you’re paying for.
- Flue and exhaust inspection
- Fan operation and current draw
- Heat exchanger condition and scale check
- Water flow rate through the unit
- Carbon monoxide test
Can you keep using it?
No. A thermal fuse trips once and stays tripped, which tells you the designers thought this was worth stopping the appliance for. Leave it off until a gas fitter has looked at it.
What the fix usually involves
The fuse itself is a part, but replacing it without finding what cooked it just means it trips again. We find the cause first. On an older unit with a scaled heat exchanger, replacement is often the honest answer.
Is it worth fixing?
That depends almost entirely on how old the unit is. Past about ten years on hot water and gas heating, and twelve on aircon, a significant repair usually costs more per remaining year than a replacement does — and it’s the same point at which the VEU rebate is worth the most, because old inefficient appliances are exactly what the scheme pays to remove. If yours is young and the fault is a component, we’ll fix it and say so.
Repair or replace? The 10-year rule, and what the rebate is worth →