Remeha Boiler Error Code E.04.08
With E.04.08 the safety input has opened via the air pressure switch. Often the flue is restricted, for example by a blocked siphon. Check the outlet outside; the flue itself is a job for an installer.
Also shown as: E04.08
Applies to: Remeha Ace platform (Tzerra Ace, Calenta Ace, Avanta Ace)
Common causes
- Excess pressure in the flue: a non-return valve that does not open, or a blocked or empty siphon
- Blockage in the air inlet or flue outlet
- Fouled heat exchanger
- Poor connection in the wiring
What to check, in order
- Check outside whether the flue outlet is clear of blockages.
- Note the code and reset the boiler once.
- If the code returns, call an installer; the siphon and the flue must be checked from inside.
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.04.08, 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
Air pressure differential switchSiphon
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.04.08
What does E.04.08 mean on a Remeha boiler?
E.04.08 means: The safety input is open (air pressure differential switch operated). With E.04.08 the safety input has opened via the air pressure switch. Often the flue is restricted, for example by a blocked siphon. Check the outlet outside; the flue itself is a job for an installer.
Can I fix Remeha E.04.08 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.04.08?
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.