Lockout due to loss of continuous flame signal
The 43 error code on Immergas boilers indicates lockout due to loss of continuous flame signal.
Immergas 43 means: lockout due to loss of continuous flame signal. On this component the documented failure modes are this occurs if the "flame signal loss (38)" error occurs 6 consecutive times within a period of 8.5 minutes, occurs if the "flame signal loss (38)" error occurs several consecutive times within a pre-established time or no gas reaching the burner, or the gas supply is shut off. A Gas Safe registered engineer should diagnose the root cause.
What Does 43 Mean
The 43 code is shown by the boiler’s control board when it detects lockout due to loss of continuous flame signal. 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 43 and the boiler stops until the fault is cleared |
Common Causes
The first cause below is the one the Immergas service literature publishes for this code (source: centriassistenza.org). The others are the failure modes documented for the same component on other boilers, confirmed by 6 different manufacturers.
| Cause |
|---|
| This occurs if the "Flame signal loss (38)" error occurs 6 consecutive times within a period of 8.5 minutes |
| Occurs if the "Flame signal loss (38)" error occurs several consecutive times within a pre-established time |
| No gas reaching the burner, or the gas supply is shut off |
| Flue or air intake blocked or restricted |
| Ignition or detection electrode dirty, worn or out of position |
| Faulty gas valve, or its wiring and connector |
Safety Warning
43 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. Guasto legato al gas. Non aprire il rivestimento della caldaia e non tentare di riparare la valvola del gas, il bruciatore, il sistema di accensione o il condotto fumi. Ripristini ripetuti sono pericolosi. La diagnosi e la riparazione devono essere effettuate da tecnico qualificato.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
How to Fix It
Press the Reset button, the boiler carries out a post-ventilation cycle before restarting
Press the Reset button, the appliance carries out a post-ventilation cycle before restarting
Check that the gas service valve is open and that other gas appliances in the property work. If they do not, the problem is the gas supply, not the boiler.
Inspect the flue and air intake along their whole length, including the outside terminal, and clear any obstruction or debris.
Inspect the ignition and detection electrode: clean off any deposits, check the gap and position against the manual, and replace it if it is worn.
Check the gas valve connector and wiring for continuity, then test the valve coil resistance against the manual; replace the valve if it is out of range.
Refer to the Immergas service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Immergas models that can display fault code 43:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Immergas models | — | Possible |
Frequently Asked Questions
Press the Reset button, the boiler carries out a post-ventilation cycle before restarting. According to the technical documentation, this is the first check on the list for 43.
43 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.