What it means
Daikin's user reference guide calls AH a warning. Daikin's service manual says it is raised if the disinfection temperature isn't reached within 6 hours or isn't held for long enough, and that the unit doesn't stop.
What to check, in order
- Avoid hot water use during the cycle
Daikin's installer reference guide lists hot water being used during disinfection, or a large amount being used just before it starts, as possible causes.
- Leave tank heating switched on
Daikin's guide says switching tank operation off while disinfection is running also causes AH.
- Ask about the start time
Daikin recommends starting disinfection when no hot water will be used for the next 4 hours. The start time is in the installer settings, so ask your installer to move it if needed.
- Let it clear itself
Daikin UK says the AH fault clears itself once the disinfection function completes.
When to call your installer
If AH keeps coming back even when no hot water is used during the cycle, ask your installer to check the settings. Daikin's service manual lists the backup heater being restricted or not allowed during disinfection, and faulty booster heater settings. Daikin's user reference guide says AH appears if the tank's anti-legionella heater is restricted during disinfection.
Quick answers
What does the Daikin Altherma AH-00 error code mean?
The regular hot water tank disinfection cycle didn't reach or hold its target temperature. The heat pump keeps running. Daikin's user reference guide calls AH a warning. Daikin's service manual says it is raised if the disinfection temperature isn't reached within 6 hours or isn't held for long enough, and that the unit doesn't stop.
Can I fix Daikin Altherma AH-00 myself?
Very easy (A few minutes). Start with: avoid hot water use during the cycle; leave tank heating switched on; ask about the start time. If AH keeps coming back even when no hot water is used during the cycle, ask your installer to check the settings. Daikin's service manual lists the backup heater being restricted or not allowed during disinfection, and faulty booster heater settings. Daikin's user reference guide says AH appears if the tank's anti-legionella heater is restricted during disinfection.
Is Daikin Altherma AH-00 worth repairing?
Not a fault. Usually not a fault: hot water was used while the tank was being disinfected. Changing the start time normally stops it.
Checked against
- Daikin Altherma 3 R ECH2O installer reference guide, AH error and help text, p. 273 (ManualsLib copy)
- Daikin Altherma 3 R ECH2O installer reference guide, error codes overview, p. 275 (ManualsLib copy)
- Daikin Altherma 3 R ECH2O installer reference guide, error code notes, p. 277 (ManualsLib copy)
- Daikin Altherma 3 R W installer reference guide 4P496758-1B, symptoms incl. AH error, p. 88 (ManualsLib copy)
- Daikin Altherma 3 R W installer reference guide 4P496758-1B, error codes, p. 90 (ManualsLib copy)
- Daikin UK: Homeowner support
- Daikin service manual ESIE20-06A, Daikin Altherma 3 M (EBLA/EDLA), PDF (copy hosted on the OpenEnergyMonitor forum)
- Daikin Altherma low temperature split user reference guide 4P499574-1A (EHVH04/08S23DAV), 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.