PCB: Power supply card K21A,K22A Auxiliary bypass relay
The A71P error code on Daikin boilers indicates pcb: power supply card k21a,k22a auxiliary bypass relay.
Daikin A71P means: pcb: power supply card k21a,k22a auxiliary bypass relay. On this component the documented failure modes are wiring, connector or harness of the control board damaged or loose or control board (pcb) faulty. You can safely reset the boiler once — if A71P returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does A71P Mean
The A71P code is shown by the boiler’s control board when it detects pcb: power supply card k21a,k22a auxiliary bypass relay. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows A71P and the boiler stops until the fault is cleared |
Common Causes
The manufacturer does not publish a cause list for this specific code. The causes below are the failure modes documented for the same component on other boilers, confirmed by the service literature of 5 different manufacturers.
| Cause |
|---|
| Wiring, connector or harness of the control board damaged or loose |
| Control board (PCB) faulty |
Safety Warning
A71P involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
How to Fix It
Power cycle the boiler (off for 30 seconds, then on)
repair loose connections
if the PCB shows signs of water damage or burnt components, replace the PCB
ensure the replacement PCB is the correct version for the boiler model
after PCB replacement, the boiler may need recommissioning and parameter setup
Unplug and re-seat the connector of the control board, then check the harness for chafing, corroded pins and breaks in continuity.
Refer to the Daikin service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
Diagnostic Tools
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Affected Models
Daikin models that can display fault code A71P:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Daikin models | — | Possible |
Frequently Asked Questions
Power cycle the boiler (off for 30 seconds, then on). According to the technical documentation, this is the first check on the list for A71P.
A71P is not classified as a high-severity fault, so the boiler can be reset once. If A71P comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.