Daikin Boiler Error Codes: Causes & Fixes

Daikin boiler error codes appear on the display of Daikin’s D2CND combi and D2TND system gas boilers as a two-part code, such as HJ-09 or 11-64, while the status ring on the front panel blinks red. Some codes, such as low water pressure, a closed radiator valve or a temporary loss of flame, can be dealt with safely by a homeowner. Anything involving the gas valve, fan, flame detection, sensors or circuit board needs a Gas Safe registered engineer.

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This guide explains what the most common codes mean, what you can safely check yourself, how to reset the boiler and when to book an engineer. The code meanings below are taken from Daikin’s operation manual for the D2CND and D2TND wall-hung condensing boiler range.

What Do Daikin Boiler Error Codes Mean?

A Daikin boiler error code tells you why the boiler has stopped, or is running with a problem. The codes fall into three broad types:

• Temporary (blocking) errors: the boiler pauses and restarts on its own once the condition clears, for example after a flame loss during operation or a sudden rise in flow temperature.
• Lockout errors: the boiler stays off until it is reset with the Mode/Reset button, for example after repeated ignition failures or overheating.
• Warnings: the boiler keeps running, but a component such as the outdoor sensor or hot water sensor has a fault that should be checked.

When an error is active, the status LED blinks red and the code is shown on the screen. The current error code can also be viewed in the boiler’s information menu, which is useful when describing the fault to an engineer. Note the full code, including both parts, before resetting anything.

Daikin Boiler Error Codes List

The table below covers the codes in Daikin’s operation manual that homeowners are most likely to see, what each one means and what you can safely do before calling an engineer.

Code	Meaning	What You Can Safely Do
HJ-09	Low system pressure	Top up through the filling loop to 0.8 bar or the pressure your installer set, then reset
HJ-08	High system pressure	Bleed a radiator to bring the pressure back down; call an engineer if it keeps rising
11-64	Ignition did not take place	Check the gas supply is on; reset after the third failed ignition attempt
11-65	Flame stabilisation fault	Wait for the boiler to retry; reset after the third failed attempt
11-66	Flame signal lost during safety time	Call an engineer if it repeats
11-67	Flame lost during operation	Temporary; wait for the boiler to re-ignite
10-64 / 10-65	Gas valve circuit or current error	Reset once; call a Gas Safe engineer if it returns
12-64 to 12-70	Combustion (ionisation) control faults	Reset if needed; call an engineer if it returns
13-64 / 13-65	Fan speed error	Reset once; call an engineer if it returns
16-64	Flue temperature overheating	Check nothing is blocking the flue outlet outside; reset; call an engineer if it returns
JJ-64	Flue temperature sensor overheating (lockout)	Reset if needed; call an engineer if it returns
1J-64	High limit thermostat overheating	Check radiator valves are open and the pressure is correct, then reset
8H-64	Flow temperature rising too steeply	Make sure radiator valves are open; the boiler restarts after a short wait
8H-65	Flow and return temperature difference too large	Make sure radiator valves are open; call an engineer if it repeats
J6-20	Return temperature sensor overheating (lockout)	Check radiator valves and pressure, then reset
J6-21	Return temperature higher than flow temperature	No reset needed; call an engineer if it repeats
8A-46	Freeze protection sensor reading below 1°C	Wait for the code to clear as the boiler warms up
80-01	Return temperature sensor fault	Reset; call an engineer if it returns
81-01	Flow temperature sensor fault	Reset; call an engineer if it returns
HC-01	Hot water temperature sensor fault	Boiler keeps running; book an engineer
H9-01	Outdoor sensor fault	Boiler keeps running; book an engineer
E1-64	Flame detected before the burner started	Reset; call an engineer if it returns
E1-71	Permanent lockout	Call an engineer
U2-01	Supply voltage outside limits	Reset; call an engineer if it returns
U4-65	OpenTherm room thermostat connection fault	Boiler keeps running; check the thermostat (e.g. batteries) and call an engineer if it persists
UA-64 to UA-70	Control board (BCC) errors	Call an engineer

Pressure codes are the easiest to deal with yourself. If HJ-09 appears, our guide to low boiler pressure explains how to top up with the filling loop and how to look for a leak. If HJ-08 appears, see our guide on why boiler pressure is too high.

In freezing weather, a frozen condensate pipe is a common reason for a condensing boiler to stop working. If the pipe running outside is frozen, thaw it with warm (not boiling) water before resetting. Our guide to a frozen condensate pipe explains how.

How to Reset a Daikin Boiler

To reset a Daikin boiler, deal with the cause of the fault first, then press the Mode/Reset button on the control panel to clear the lockout. Daikin’s manual says to use the reset only once the cause of the error has gone.

1. Write down the full error code shown on the display.
2. Check the system pressure. It is shown on the display when the boiler is in standby. If it is low, top up through the filling loop before resetting.
3. Check the basics: the boiler has power, other gas appliances work, the thermostat is calling for heat, radiator valves are open and the condensate pipe is not frozen.
4. Press the Mode/Reset button to reset the lockout error.
5. Wait for the boiler to try to light. The LED ring flashes and then glows steadily while the burner is running.
6. If the same code comes back, stop resetting and contact an engineer.

If the boiler doesn’t respond at all, check whether it has been left in standby or full-off mode. Pressing the Mode button for five seconds switches the unit on. Our general guide on how to reset a boiler covers the same process for other brands.

When to Call a Gas Safe Engineer About a Daikin Boiler Error Code

Call a Gas Safe registered engineer if a code returns after a reset, if Daikin’s manual says to contact your service agent, or if the fault involves the gas valve, fan, flame detection, sensors or control board. By law, only a Gas Safe registered engineer can work on gas appliances, so never remove the boiler casing or attempt repairs yourself. For faults that don’t produce a code at all, our guide to common boiler problems covers the usual causes and fixes.

Codes that need an engineer include:

• 10-64 and 10-65 (gas valve circuit faults)
• E1-64 (flame detected before ignition) and E1-71 (permanent lockout)
• 13-64 and 13-65 (fan speed errors) that return after a reset
• 16-64 and JJ-64 (flue overheating) if they repeat
• 80-01, 81-01 and HC-01 (temperature sensor faults)
• UA codes (control board errors)
• HJ-09 that keeps coming back, which usually means water is escaping through a leak, the pressure relief valve or a faulty expansion vessel

If you smell gas, don’t try to reset the boiler. Turn off the gas at the meter if it is safe to do so, open windows, avoid using electrical switches and call the National Gas Emergency Service on 0800 111 999.

If repeated faults mean it’s time to replace an ageing boiler, you can get a new boiler quote online.

Daikin Boiler Error Codes: FAQs

Why Is My Daikin Boiler Showing HJ-09?

HJ-09 means the system water pressure is too low. Daikin’s manual advises increasing the pressure to 0.8 bar, so top the system up through the filling loop to that level or the pressure your installer set, then reset the boiler. If the pressure keeps dropping, there is likely a leak or a faulty pressure relief valve, and an engineer should investigate. On some other makes, the same low-pressure lockout shows up as an E1 boiler error code.

What Does 11-64 Mean on a Daikin Boiler?

11-64 means the boiler tried to light but ignition did not take place. Check that gas is reaching the property, for example that the hob works and a prepayment meter has credit. Daikin advises resetting after the third unsuccessful ignition attempt. If it fails again, call a Gas Safe registered engineer.

How Many Times Should I Reset a Daikin Boiler?

Once, or twice at most. Daikin’s manual says that if a problem repeats after a reset, you should contact your service agent. Resetting over and over without fixing the cause won’t clear the fault and delays a proper repair.

Why Does My Daikin Boiler Show an Error Code but Keep Working?

Some Daikin codes are warnings rather than lockouts. H9-01 (outdoor sensor fault), HC-01 (hot water temperature sensor fault) and U4-65 (room thermostat connection fault) all let the boiler keep running, but the faulty component should still be checked by an engineer.

Is the 8A-46 Code on a Daikin Boiler Serious?

Usually not. 8A-46 means the freeze protection sensor is reading below 1°C, so the boiler won’t run until the temperature rises, and Daikin’s advice is to wait for the code to clear. Keep the boiler switched on at the mains in cold weather, because its frost protection only works when it has power.