Siemens LME11 / LME21 / LME22 troubleshooting
The Siemens LME11, LME21 and LME22 are burner controls for 1- or 2-stage gas burners of small to medium capacity, with flame supervision by ionization probe or a QRA UV detector. LME11 is for 1-stage burners, LME21 for 2-stage burners and LME22 for 2-stage burners with actuator control. A multicolour signal lamp in the lockout reset button shows the operating state and, after a lockout, the cause as a red blink code.
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How it reports faults
- After a non-alterable lockout the red signal lamp lights up steadily, and the lockout is kept through a mains failure.
- Press the lockout reset button for more than 3 seconds to start visual diagnostics: the lamp flashes red and the number of blinks is the error code. Pressing it again for at least 3 seconds switches to interface diagnostics (red flicker light) for the OCI400 interface and ACS410 software; press again for at least 3 seconds to leave it.
- Press the lockout reset button for about 1 second (less than 3 seconds) to reset. The LME can only be reset when all contacts in the line are closed and there is no undervoltage.
- During startup the lamp shows the operating state: off in the waiting time, yellow for the air pressure switch waiting phase and prepurge, flashing yellow for ignition, green for flame ok, flashing green for flame not ok, green-red for extraneous light, yellow-red for undervoltage.
- The alarm output at terminal 10 is ON for every blink code except 10 blinks.
- Siemens says to press the reset button only by hand, with no tools or pointed objects.
Operating sequence
- A: Start commandThe control thermostat or pressurestat calls for heat. All line contacts must be closed, the air pressure switch in its no-load position and the flame detector dark.
- tw: Waiting timeAbout 2.5 s. The lamp is off.
- t10: Air pressure signalThe fan runs and the air pressure switch must signal air within the specified time (5 s on LME11/LME21 types, 3 s on LME22 types). LME22 also drives the actuator open (t11) and closed (t12) around prepurge.
- t1: Prepurge timeMinimum 7 to 50 s depending on type (for example 20 s on LME21.230C2, 30 s on LME21.330C2). The lamp is yellow.
- t3: Preignition timeIgnition on before fuel: about 2 s (LME11/LME21) or 3 s (LME22). The lamp flashes yellow.
- TSA: Safety timeFuel valve 1 opens and flame must be established (B–B´): maximum 3 s, or 5 s on some LME21 types. No flame by the end gives 2 blinks.
- t3n / t4: Postignition and second stageIgnition stays on for the postignition time; after the interval t4 (about 8 or 10 s) fuel valve 2 is released on LME21 and LME22.
- C–D: Burner operationOperating position reached; the burner generates heat with the flame supervised (green lamp). D is the controlled shutdown by the thermostat or pressurestat. After at most 24 hours of continuous operation the LME makes a controlled shutdown and restart.
Fault codes
| Code | Name |
|---|---|
| 2 | No establishment of flame at the end of safety time (TSA) |
| 3 | Air pressure switch faulty |
| 4 | Extraneous light when burner is started up |
| 5 | Air pressure switch time supervision |
| 7 | Too many losses of flame during operation (limitation of repetitions) |
| 10 | Wiring error or internal error, output contacts, other faults |
| 6 | Free (not used) |
| 8–9 | Free (not used) |
| 14 | CPI contact not closed (types with a closed position indicator input) |
Evidence to collect
- The red blink count read after pressing reset for more than 3 seconds
- Full LME type number from the label (e.g. LME22.331C2)
- Lamp colour during the last start
- Ionization or UV detector current during a normal start
Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.