Siemens LME 7 blinks: flame loss during operation, what to check?
My burner control, a Siemens LME, is showing 7 red blinks. The flame establishes, but then drops out during operation, leading to a lockout. What should I check first?
A Siemens LME control showing 7 red blinks indicates too many losses of flame during operation. This means the flame was established but then lost while the burner was running, exceeding the allowed repetitions. For LME11 types, this can happen after up to 3 repetitions, while LME2 types result in a non-alterable lockout without repetition.
Likely causes and checks
1Faulty or soiled flame detector
- Points to it
- The flame detector might be dirty or malfunctioning, causing an unreliable flame signal. This is often indicated if the green lamp flashed (flame not ok) during operation before the lockout, or if the ionization current is near the threshold.
- Check
- Measure the ionization current during operation. For an ionization probe, ensure the current is above DC 3 µA for reliable operation and ideally above DC 5 µA to prevent the green lamp from flashing. Clean or reposition the probe, and inspect its ceramic insulator and the burner earthing.
2Faulty or soiled fuel valves
- Points to it
- Issues with the fuel valves, such as dirt or malfunction, can lead to the flame dropping out. This might be accompanied by valve noise or a drop in gas pressure at the burner while the valve is open.
- Check
- Check the gas pressure downstream of the valves during operation. Also, inspect the valve coils and their wiring for any faults.
3Gas supply pressure dropping
- Points to it
- An insufficient or fluctuating gas supply pressure can cause the flame to be lost, especially during load changes or when other gas users start.
- Check
- Trend the gas inlet pressure across a full firing cycle and compare it against the burner's minimum required pressure.
4Poor adjustment of burner
- Points to it
- Incorrect burner adjustments can lead to an unstable or lifting flame, causing it to drop out. This is often observed after a service or if losses occur only at a specific stage of operation.
- Check
- Have the burner set up across both stages using a combustion analyzer. Check the air damper and, if applicable for LME22, the actuator settings.
Next check: Start by checking the flame detector, as a flashing green lamp before lockout strongly points to a flame signal issue rather than a fuel supply problem. Measure the ionization current and clean or reposition the probe if necessary.
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