Remeha Boiler Error Code H.03.05
H.03.05 is an internal blocking of the gas valve control. Restarting can be tried; if it returns, the CU-GH PCB must be replaced by an installer.
Also shown as: H03.05
Applies to: Remeha Ace platform (Tzerra Ace, Calenta Ace, Avanta Ace)
Common causes
- Fault in the safety core of the control
- Faulty CU-GH PCB
What to check, in order
- Note the full code and do not keep resetting the boiler.
- Only check the water pressure and whether the gas tap is open; do not open the boiler.
- If the code stays or returns, call a qualified 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
This code usually points to a faulty part, wiring or the control board on a Remeha boiler. Run the checks above to rule out the simple causes, then book a technician — and book one straight away 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 H.03.05, 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.
Repair or replace?
This fault is in professional territory: the fix usually means a major part or board-level work, and the labour adds up. If your machine is already well into its service life, get the repair quote first, then compare it with the price of a current equivalent model before you decide. Paying a large share of a new machine's price to repair an old one is rarely the better deal; replacing a machine over one cheap fault is wasteful too.
Parts that may be involved
CU-GH PCBGas valve
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 H.03.05
What does H.03.05 mean on a Remeha boiler?
H.03.05 means: Internal blocking in the gas valve control (fault in the safety core). H.03.05 is an internal blocking of the gas valve control. Restarting can be tried; if it returns, the CU-GH PCB must be replaced by an installer.
Can I fix Remeha H.03.05 myself?
Only the preliminary checks. Code H.03.05 usually means a part, wiring or the control board has failed, which is a technician job. Run the checks to rule out simple causes before you book.
How do I clear Remeha H.03.05?
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.