Burner Fault Codes and the 7 Most Common Faults (Siemens, Honeywell, Brahma)

Safety first: how many times can you press reset?

Two or three times consecutively at most. Every reset attempt makes the burner try to open fuel again. If ignition fails, a further quantity of unburnt fuel enters the combustion chamber on each attempt. Repeated resets are therefore a genuine explosion risk.

Also worth knowing:

• A safety lockout is retained in memory even after a power failure. Switching the supply off and on does not clear the fault; it only makes the record harder to read.
• If the same fault recurs quickly, stop resetting. A repeating lockout is not a coincidence — it is the signature of a degraded component.
• If there is a smell of gas in the plant room, do not operate any electrical equipment. Close the main gas valve, ventilate the space and call the gas emergency line.

Which control box is fitted? Brand-to-control-box mapping

The table below shows the pairings most often encountered in the field. The definitive answer is always the label on the control box — within a single brand, the control box varies by model and year of manufacture.

This is why searching for a single "[brand] fault code table" is misleading. The right question is: which control box is fitted to this burner?

Siemens LME / LMO fault codes (red LED blink code)

On Siemens LME (gas) and LMO (oil) control boxes, faults are signalled by the number of repeated blinks of the red LED in the reset button. The LED flashes a set number of times, pauses briefly, then repeats the same sequence. Counting the blinks is the whole diagnosis.

The most important distinction is between 2× and 4×. Both present as "it won't light", but the root causes differ: 2× lies in the fuel or ignition chain, while 4× can indicate a leaking valve. If 4× recurs, the plant should not be operated until a valve tightness test has been carried out.

Blink counts apply to common models in the LME/LMO family. Verify against the datasheet for the specific control box before commissioning; minor differences exist between sub-models.

Siemens LMV series (AZL display) fault codes

The LMV2x/LMV3x and LMV5x show an alphanumeric code on the AZL display rather than a single LED pattern. Two pieces of information appear:

• Error / Loc code: the main fault class
• Diagnostic code: the specific cause within that class

Both must be read together — the main code alone gives an incomplete picture. Several main codes follow the same logic as the LME family:

The LMV3x and LMV5x add separate code groups for actuator position errors, fuel–air ratio control faults, O₂ trim faults and parameter/CRC errors. These must be read from the manufacturer's datasheet, and intervention should be left to an authorised service engineer: an incorrect parameter change on an LMV directly affects both the combustion setting and the safety functions.

Reading faults on Honeywell–Satronic control boxes

There is an important difference in this family: most TF, DKG, DKO and DMG series units have no blink code. There is a single red lockout lamp on the reset button, which tells you the unit has locked out but not why.

Diagnosis is therefore made by measurement:

1. Measure the flame signal. A microammeter is connected in series between the control box and the ionisation probe.
2. Check gas and air pressure switch contacts to follow the interlock chain step by step.
3. Verify ignition transformer output and electrode gap.
4. Confirm live/neutral orientation and earthing (see fault 2 below).

Newer digital models such as Honeywell's MMI series do provide LED-based diagnostic codes. Always confirm the code table against the manufacturer's datasheet for the exact model number on the label.

Brahma (CM, SM, TDG series) and Riello's own control boxes (RMG/RMO) also carry model-specific LED indication; on Riello units, holding the reset button for a few seconds typically starts a visual diagnostic sequence.

The 7 most common burner faults

These seven account for the large majority of service calls. For each: the symptom, the causes, and the correct approach.

1. No flame established at end of safety time

Symptom: the burner runs the fan, completes pre-purge, there is a brief click, and it locks out. 2× blinks on Siemens.

Causes:

• Gas pressure below the minimum threshold (regulator, blocked filter, undersized pipework, several appliances firing simultaneously)
• Burnt safety valve coil, or valve mechanically failing to open
• Ignition electrode gap, angle or height has drifted; cracked ceramic insulator
• Faulty ignition transformer or HT lead
• Mixture too lean at ignition position — too much air, mixture will not catch
• On oil: blocked or coked nozzle, low pump pressure, air in the fuel line

Correct approach: electrode gap and position must be set to the manufacturer's stated dimensions. "Roughly right" electrode setting is the single most frequent source of repeat call-outs.

2. Weak or absent ionisation (flame) signal

Symptom: the flame is visibly present but the burner still locks out — usually flame loss during operation (7× blinks) first, then full lockout.

Causes:

• Ionisation probe fouled with soot or oxide
• Cracked ceramic insulator, so the signal leaks to earth
• Poor or missing chassis earth
• Live and neutral reversed. Ionisation measurement is referenced to neutral; with the supply reversed the signal collapses even though the flame is present. This is the classic cause of "unexplained" faults appearing straight after other work on the panel.
• Distorted flame geometry — the probe is not properly immersed in the flame
• Excess air pushing the flame away from the probe

Correct approach: always measure the signal with a microammeter. Most control boxes require a minimum of around 1 µA; a healthy installation typically reads 4–8 µA (the exact threshold is stated in the datasheet). Thresholds for photocells and UV cells on oil burners are different.

3. Air pressure switch fault

Symptom: lockout after pre-purge, before ignition. 3× or 5× blinks on Siemens.

Causes:

• Impulse hose blocked, cracked or fitted to the wrong port
• Fan impeller and intake grille clogged with dust, reducing pressure
• Incorrect switch setting (adjusted by trial and error after previous work)
• Welded contact — this is what 5× blinks indicates
• Plant room fresh-air louvre closed or undersized, which is both common and dangerous

Correct approach: the switch setting is not arbitrary; it is derived from the fan pressure measured at commissioning. If the louvre is blocked, open the louvre — do not lower the switch setting to compensate.

4. Low gas pressure switch alarm

Symptom: the burner will not start at all, or drops out when it steps up to high fire.

Causes:

• Blocked gas filter
• Regulator out of adjustment or ruptured diaphragm
• Undersized pipework; multiple appliances drawing simultaneously
• Seasonal drop in network pressure
• Failed pressure switch

Correct approach: pressure must be measured with the burner running at high fire. Static pressure can look perfectly normal and still collapse under load.

5. Extraneous light

Symptom: the burner locks out before it starts. 4× blinks on Siemens.

Causes:

• Leaking safety shut-off valve with residual flame in the chamber — the critical scenario
• Hot refractory glow being read as flame by a UV cell or photocell
• Damp photocell or leakage in its wiring
• External light entering through the detector housing

Correct approach: test valve tightness first. If the detector is simply swapped out as "faulty" and a leaking valve is missed, the real hazard remains in place.

6. Fan motor and electrical faults

Symptom: the burner does not turn at all, runs noisily, or trips the overload.

Causes:

• Overload set incorrectly, or burnt contactor contacts
• Worn bearings causing vibration and noise
• Weak run capacitor on single-phase motors
• Phase loss on three-phase motors
• Dirt build-up on the impeller causing imbalance and raised current

Correct approach: measure motor current on all three phases and check for imbalance. A dirty impeller does not only raise current — it reduces air volume and therefore corrupts the combustion setting.

7. Flame loss during operation

Symptom: the burner lights normally, runs for a while, then locks out. 7× blinks on Siemens.

Causes:

• Fuel–air ratio at the margin, so the flame is unstable at high fire
• Insufficient or excessive chimney draught; wind-induced back pressure
• Gas pressure fluctuating under load
• Diffuser position shifted or fouled
• Marginal ionisation signal (assess together with fault 2)
• On oil: coked nozzle, water or sludge in the fuel

Correct approach: this fault is almost always diagnosed with a flue gas analyser. Any adjustment made without measuring O₂, CO and flue gas temperature across all firing rates is a temporary fix.

Which faults are urgent?

The only way to stop faults recurring: planned maintenance

Most of the seven faults above do not appear suddenly. Electrode erosion, filter blockage, impeller fouling and pressure switch drift develop over months — efficiency degrades first, lockouts follow. For intervals and a full checklist see how often burner maintenance should be carried out, and for the underlying operating logic see what a burner is and how it works.

Safety notice: work on the gas train, ignition circuit and combustion settings must be carried out by trained and authorised technical personnel only. Unauthorised changes to control box parameters can disable safety functions.