Flame sensed with no call for heat: usually a slow-closing or leaking gas valve
The 5-FLASH error code on Daikin boilers indicates flame sensed with no call for heat: usually a slow-closing or leaking gas valve.
Daikin 5-FLASH means: flame sensed with no call for heat: usually a slow-closing or leaking gas valve. The usual causes are gas valve coil failure (electrical fault), gas valve stuck closed or partially open or gas supply interrupted (prepayment meter, emergency control valve). A Gas Safe registered engineer should diagnose the root cause.
What Does 5-FLASH Mean
The 5-FLASH code is shown by the boiler’s control board when it detects flame sensed with no call for heat: usually a slow-closing or leaking gas valve. 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 5-FLASH and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 2 technical sources.
| Cause |
|---|
| Gas valve coil failure (electrical fault) |
| gas valve stuck closed or partially open |
| gas supply interrupted (prepayment meter, emergency control valve) |
| incorrect gas pressure (too high or too low) |
| gas valve wiring fault |
| PCB not sending open signal to the gas valve |
Safety Warning
5-FLASH is a gas-related fault. Never attempt to repair or adjust the gas valve, burner assembly, or flue system yourself. All gas work must be carried out by a Gas Safe registered engineer (UK) or licensed HVAC technician (US). Repeated resets after ignition failure can cause unburnt gas to accumulate inside the combustion chamber — this is a serious safety hazard. If you smell gas at any point, turn off the gas supply at the meter, open windows, leave the property, and call your gas emergency service immediately. Gas-related fault. Do not open the furnace cabinet or work on the gas valve, burner, igniter or venting yourself. Repeated resets are unsafe. Have it diagnosed and repaired by a licensed HVAC technician.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
Check the gas supply — verify the gas meter is on and other gas appliances in the property work
Check the gas isolation valve at the boiler is fully open
Measure the inlet gas pressure at the boiler test point — should be 20 mbar (8.0 in wc) for natural gas (UK)
During ignition, measure the voltage at the gas valve coil terminals — the PCB should send a signal
If the valve receives voltage but does not open, the gas valve is faulty
Check the gas rate at the meter against the manufacturer's data
How to Fix It
Restore the gas supply if interrupted
replace the gas valve if it is stuck or electrically faulty — Gas Safe registered engineer only
adjust gas pressure if out of specification
repair wiring between gas valve and PCB
if PCB is not sending signal, replace the PCB. Warning: never attempt gas work unless you are Gas Safe registered
Refer to the Daikin service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Daikin models that can display fault code 5-FLASH:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Daikin models | — | Possible |
Frequently Asked Questions
Restore the gas supply if interrupted. According to the technical documentation, this is the first check on the list for 5-FLASH.
5-FLASH is classified as a high-severity fault: it involves gas, combustion or flue components. Do not keep resetting the boiler and do not attempt the repair yourself — call a Gas Safe registered engineer.