Siemens LME 4 blinks: extraneous light at startup, what to check?
My Siemens LME burner control is giving 4 red blinks and a green-red signal lamp during startup. This happens before the fan even starts, and the unit locks out. What should I check first for extraneous light?
A Siemens LME burner control showing 4 red blinks and a green-red signal lamp during startup indicates extraneous light. This means the flame detector reported a flame before any fuel valves opened, which is a startup precondition violation. Depending on when it occurs, it can lead to a non-alterable lockout immediately or after 30 seconds.
Likely causes and checks
1Real flame or glowing fuel after shutdown
- Points to it
- The flame detector might be seeing an actual flame or glowing fuel in the combustion chamber from a previous shutdown, indicating afterburning.
- Check
- Look into the combustion chamber for visible flame or afterburning. If flame persists after valves close, isolate the gas and have fuel valves tightness-tested by a qualified technician.
2Ignition spark arcing to the ionization probe
- Points to it
- The ignition spark could be arcing over to the ionization probe, causing the detector to falsely report a flame.
- Check
- Check the gap and position of the ignition electrode and probe against the burner manual to ensure the spark cannot arc to the probe.
3Aged or faulty UV detector (QRA)
- Points to it
- If using a UV-supervised burner, the detector itself might be faulty or aged, reporting a flame even in a cold, dark chamber.
- Check
- Cover the QRA and check if a flame is still reported. The data sheet describes a UV test for aged cells after a controlled shutdown. Replace a detector that falsely sees light.
4Interference on the detector cable
- Points to it
- The detector cable might be picking up electrical interference if it's run too close to mains or ignition cables, or if it's too long.
- Check
- Ensure the detector cable is separate and not run with other cables, and that it is within the permitted length as per the data sheet. Reroute if necessary.
Next check: Start by visually inspecting the combustion chamber for any signs of residual flame or glowing fuel from a previous shutdown. This is often the most direct and easiest initial check for 'extraneous light'.
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