Siemens LME21 2 blinks: No flame at end of safety time, what to check?
My industrial gas burner with a Siemens LME21 controller is giving 2 red blinks. It happens right at light-off, and I don't hear or see a spark. What should I check first?
A Siemens LME21 controller displaying 2 red blinks indicates that no flame was established by the end of the safety time (TSA) after the fuel valve opened and ignition was attempted. This is a non-alterable lockout on LME2… type controllers. The issue typically occurs during the initial light-off sequence after a call for heat or maintenance work on the gas train or electrodes.
Likely causes and checks
1Faulty ignition equipment
- Points to it
- The burner control opened fuel valve 1 and ignited, but the flame detector did not report a flame before the safety time (TSA) ended. If no ignition spark is heard or seen during preignition and the safety time, the ignition equipment is a likely cause.
- Check
- With power isolated, inspect the ignition electrode, its gap, and insulator, as well as the ignition cable. Have the ignition transformer output checked per the burner manual.
2No fuel, or faulty or soiled fuel valves
- Points to it
- If a spark is present but no flame appears, or if the gas supply has been recently disturbed, there might be an issue with fuel delivery. The controller is attempting to establish a flame but is failing to do so.
- Check
- Confirm the manual gas cock is open and measure gas pressure at the burner during the safety time. Check that fuel valve 1 opens when energized.
3Poor adjustment of burner
- Points to it
- If a flame starts but is unstable or late, leading to a lockout, especially after recent burner adjustments or work on the nozzle/head, the burner's settings may be incorrect.
- Check
- Check the start gas rate and air setting against the burner maker’s commissioning data with a combustion analyzer.
4Faulty or soiled flame detector (ionization probe)
- Points to it
- If a flame is visible through the sight glass but the burner still locks out at the end of TSA, the flame detector might not be correctly sensing the flame.
- Check
- Measure the ionization current with a DC microammeter in the measuring circuit shown in the data sheet. Check the probe position, ceramic insulator, and burner earthing.
Next check: Given that you don't hear or see a spark, the first step should be to inspect the ignition equipment. Isolate power and check the ignition electrode, its gap, insulator, and cable. Also, consider having the ignition transformer output checked.
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