Siemens LME11 / LME21 / LME22 fault 2: No establishment of flame at the end of safety time (TSA)
Two red blinks mean the burner control opened fuel valve 1 and ignited, but the flame detector did not report a flame before the safety time (TSA) ended. On LME2… types this is a non-alterable lockout at the end of the safety time. LME11… types first repeat the startup up to 3 times per controlled startup before locking out.
Diagnose this with AI
Try Free Boiler Diagnostic Upload a keypad photo, the fault history or a parameter export from your Siemens LME11 / LME21 / LME22. InduQT compares the evidence and suggests the next useful checks.
When it happens
- Safety time (TSA), the interval for establishment of flame (B–B´) after preignition
- Usually at the first light-off after a call for heat, or after work on the gas train or electrodes
Where it sits in the burner
Supervised functions: Ignition and pilot, Flame supervision, Main fuel delivery.
| Component | Signals to look at | How it fails |
|---|---|---|
| Ignition transformer and electrode | Ignition output | Igniter electrode wear or wrong gap; Ignition transformer or lead failure |
| Main safety shutoff valves | Main fuel valve output, Valve proof of closure | Fuel valve not opening fully; Valve seat leakage or slow closing; Welded, jumpered or miswired contact |
| Fuel supply and regulator | Main gas pressure, Oil pressure | Fuel supply pressure droop; Regulator out of adjustment or sticking |
| Flame rod | Flame signal | Flame rod or burner ground fault; Scanner no longer sighted on the flame root |
| Flame scanner (UV / IR) | Flame signal | Dirty or fogged scanner sight path; Electrical noise on signal wiring; Scanner no longer sighted on the flame root; Detector or amplifier ageing |
| Burner management controller | Burner sequence state, Controller supply voltage | Electrical noise on signal wiring; Controller internal fault; Supply voltage, frequency or grounding problem; Configuration or commissioning data changed |
Likely causes and checks
1Faulty ignition equipment
- Points to it
- No ignition spark heard or seen during preignition and the safety time.
- Check
- With power isolated, inspect the ignition electrode, its gap and insulator and the ignition cable; have the ignition transformer output checked per the burner manual.
2No fuel, or faulty or soiled fuel valves
- Points to it
- Spark present but no flame; gas cock closed, gas pressure switch or supply recently disturbed.
- 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 energised.
3Poor adjustment of burner
- Points to it
- Flame starts but is unstable or late; lockout follows a burner adjustment or nozzle/head work.
- Check
- Check start gas rate and air setting against the burner maker’s commissioning data with a combustion analyser.
4Faulty or soiled flame detector (ionization probe)
- Points to it
- Flame visible through the sight glass but the burner still locks out at the end of TSA.
- Check
- Measure the ionization current with a DC microammeter in the measuring circuit the data sheet shows. For an ionization probe the data sheet gives a switching-on threshold of DC 1.5 µA, a detector current of DC 3 µA for reliable operation, and about DC 5 µA as the threshold below which the green lamp flashes (flame not ok) during operation. Check probe position, ceramic insulator and burner earthing.
5Ignition spark disturbing the ionization signal
- Points to it
- Flame present, ionization current low during the ignition phase only.
- Check
- The data sheet notes ignition can disturb ionization current at startup: check and optimise the probe position, and it may help to swap phase and neutral on the primary side of the ignition transformer.
6Faulty or soiled UV detector (QRA with AGQ3…A27)
- Points to it
- UV-supervised burner; flame visible but not detected.
- Check
- Clean the QRA sight path and measure the UV detector current at the QRA (minimum 200 µA required per the data sheet).
Telling it apart
- 2 blinks is a flame that never proved during the safety time. 7 blinks is a flame that proved and was later lost during operation.
- If the burner does not even reach ignition (no fan, no prepurge), the cause is earlier in the sequence: look at the line contacts, air pressure switch (3 or 5 blinks) or extraneous light (4 blinks).
- On an LME11 the burner retries up to 3 times before 2 blinks; an LME21 or LME22 locks out on the first failed safety time.
Evidence to collect
- The blink count read after pressing the reset button for more than 3 seconds
- LME type from the label (e.g. LME21.330C2) and its safety time
- Whether a spark and a flame were seen during the start
- Gas pressure at the burner during the safety time
- Ionization or UV detector current
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.