What it means
Daikin's guides call it a "Zero cross detection problem". Its service manual says the unit stops and the code is reset at the controller or by a power reset.
What to check, in order
- Check for a power problem
Daikin's service manual lists power drops among the causes. Check whether there has been a power cut, or whether a circuit breaker for the heat pump has tripped.
- Try one power reset
Daikin's service manual says A1-00 can be cleared with a power reset. Daikin UK's user guide says to switch the power off, wait 60 seconds, then turn it back on. If the code comes back, call your installer.
- Read the help text
On the controller, open the main menu and choose Malfunctioning to see the code and a short description. The help button gives a longer one. Note the code for your installer.
When to call your installer
If it returns, call your installer. Daikin's service manual lists a faulty main PCB, a faulty noise filter PCB, or power supply problems such as an imbalance of more than 4%, a power drop or a short circuit.
Quick answers
What does the Daikin Altherma A1-00 error code mean?
The outdoor unit's board isn't reading the mains supply properly, so the heat pump has stopped. Daikin links it to power supply problems or a board fault. Daikin's guides call it a "Zero cross detection problem". Its service manual says the unit stops and the code is reset at the controller or by a power reset.
Can I fix Daikin Altherma A1-00 myself?
Easy (about 5 minutes). Start with: check for a power problem; try one power reset; read the help text. If it returns, call your installer. Daikin's service manual lists a faulty main PCB, a faulty noise filter PCB, or power supply problems such as an imbalance of more than 4%, a power drop or a short circuit.
Is Daikin Altherma A1-00 worth repairing?
Get a quote first. A one-off after a power drop may clear with a reset. If it keeps coming back, a board or supply fault needs an engineer, so get a quote.
Checked against
- Daikin Altherma 3 R W installer reference guide 4P496758-1B (ERGA-D, EHBH/EHBX-D), troubleshooting and error codes, p. 89 (ManualsLib copy)
- Daikin Altherma 3 R ECH2O installer reference guide, error codes overview, p. 274 (ManualsLib copy)
- Daikin service manual ESIE20-06A, Daikin Altherma 3 M (EBLA/EDLA), PDF (copy hosted on the OpenEnergyMonitor forum)
- Daikin UK: Daikin Altherma Low Temperature Split Heat Pump user guide (2015), PDF
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.