What it means
Older Daikin service manuals call it insufficient gas. Daikin's US service manual says the unit watches things like input current and discharge pipe temperature to spot it, and shuts down if the error repeats.
What to check, in order
- Note the code and model
Write down the code and the full model name. Daikin's European guides ask you to give your installer the symptoms, the model name and the installation date.
- Mention any recent work
Daikin's service manual lists a closed stop valve and leaks at the pipe joints among the checks. If the unit was just installed or moved, tell the installer.
- Don't keep resetting it
Daikin's European user guides say the cause should be dealt with before the code is reset, by a licensed installer or dealer.
When to call an engineer
Call an F-gas certified engineer in the UK or an HVAC technician in the US. Daikin's service manual has them check for a closed stop valve, oil marks at the pipe joints that point to a leak, cracked pipework and the thermistors, then charge the specified amount of fresh refrigerant.
A repair visit will usually check the refrigerant charge and the pipe joints for leaks, which needs a qualified refrigeration engineer.
- Note the model and serial number. They're on a label on the side of the indoor unit, and on the outdoor unit.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Daikin U0 error code mean?
The system has worked out that not enough refrigerant is circulating, so it can't cool or heat properly and may shut down. Older Daikin service manuals call it insufficient gas. Daikin's US service manual says the unit watches things like input current and discharge pipe temperature to spot it, and shuts down if the error repeats.
Can I fix Daikin U0 myself?
Engineer only (engineer visit). Start with: note the code and model; mention any recent work; don't keep resetting it. Call an F-gas certified engineer in the UK or an HVAC technician in the US. Daikin's service manual has them check for a closed stop valve, oil marks at the pipe joints that point to a leak, cracked pipework and the thermistors, then charge the specified amount of fresh refrigerant.
Is Daikin U0 worth repairing?
Get a quote first. Finding a leak, repairing it and recharging needs an engineer. Get a quote, especially on an older system.
Checked against
- Daikin Service Manual SiUS042113E, FTXM-V / RXM-V inverter pair wall mounted type (manualslib copy of the Daikin PDF)
- Daikin Service Manual SiUS04-924_A, RXS / FTXS H-series inverter pair wall mounted type (PDF)
- Daikin: Simple Self-Diagnosis by Malfunction Code, SM-TS3, list of error codes (PDF)
- Daikin CTXA / FTXA User reference guide 4PEN518786-10V, English (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.