Remeha Boiler Error Code E.04.03
E.04.03 is a safety lockout: the temperature has risen above the limit, almost always because of too little flow. Check the pressure and bleeding and reset once; if it returns, an installer must check the pump and the heat exchanger.
Also shown as: E04.03
Applies to: Remeha Ace platform (Tzerra Ace, Calenta Ace, Avanta Ace)
Common causes
- No or too little flow: air in the system, low water pressure or a pump that is not running
- Fouled heat exchanger
What to check, in order
- Check the water pressure and top up to about 1.5 to 2 bar if needed.
- Bleed the system and open the radiator valves.
- Reset the boiler once; if the code returns, call an installer.
Clear the code and test
- Fix what the checks above found first — pressure topped up, a radiator bled, the thermostat set right. Resetting without fixing the cause only brings the code back.
- Make sure the boiler has power and the gas tap at the boiler is open.
- If the water pressure is below 1.5 bar, top it up to between 1.5 and 2 bar with the filling loop, as your manual shows.
- Press the reset button once and watch a full cycle: the boiler should start, heat the radiators or the tap water, and keep running without the code coming back.
When to call a professional
Most cases are solved by the checks above. Book a technician if any of these apply:
- The code comes back after you have run the checks and a test cycle.
- You smell burning, see sparks or scorch marks, or the breaker trips.
- Water is leaking and you cannot stop it.
- The fix needs panels opened beyond what your manual describes, or a part tested with a meter, and you are not set up for that.
When you call, give the brand, the code E.04.03, your model number (on a label on the type plate, usually at the bottom or on the side of the boiler) and the checks you already ran. It shortens the visit.
Parts that may be involved
Heat exchangerCirculation pump
Parts are model-specific. Find your model number first — usually on a label on the type plate, usually at the bottom or on the side of the boiler — and match the part to that number before ordering.
Questions people ask about E.04.03
What does E.04.03 mean on a Remeha boiler?
E.04.03 means: The measured temperature is above the safety limit. E.04.03 is a safety lockout: the temperature has risen above the limit, almost always because of too little flow. Check the pressure and bleeding and reset once; if it returns, an installer must check the pump and the heat exchanger.
Can I fix Remeha E.04.03 myself?
Start yourself: the checks on this page cover the causes you can reach without opening the machine up. If they point to a faulty part, testing or replacing it is usually a technician job.
How do I clear Remeha E.04.03?
Fix what the checks above found first — pressure topped up, a radiator bled, the thermostat set right. Resetting without fixing the cause only brings the code back. Make sure the boiler has power and the gas tap at the boiler is open. If the water pressure is below 1.5 bar, top it up to between 1.5 and 2 bar with the filling loop, as your manual shows.
Sources checked
The meaning and checks for this code were checked against the sources above in November 2026. Codes vary by model and region; if your manual lists a different meaning for your exact model, follow the manual.