Landis & Gyr LFL1.635 Burner Control Unit
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Product Information
The Landis & Gyr LFL1.635 is an electromechanical burner control unit from the LFL series designed for the control and supervision of medium to high-capacity forced draft gas, oil, or dual-fuel burners in intermittent operation. Operating on a 230 V AC supply at 50/60 Hz with an IP40 protection rating, this controller manages automatic burner sequence timing across industrial boiler and commercial thermal heating installations. Built around electromechanical switching cams, the unit delivers continuous sequence control without relying on programmable digital microcontrollers.
Physical installation relies on a plug-in chassis design that mates directly into standard AGM410011000 or AGM11 plug-in base units. Replacement does not require rewiring of the terminal base or software programming, as all timing profiles—including a 66-second pre-purge period and a 2.5-second ignition safety time—are defined internally by the physical mechanism. The LFL1.635 interfaces with air damper actuator drives and limit contacts at terminals 4 and 8, as well as air pressure switch interlocks at terminals 6 and 14. Flame monitoring is compatible with ionization probes, photocells, and Siemens or Landis & Gyr UV detectors such as the QRA2, QRA10, and QRA4.a series. When swapping out a faulty module in an existing burner panel, ABC Industrial Parts can supply tested replacement units to restore system operation without requiring field configuration.
Diagnostic information is visible on the front cover through a transparent inspection window revealing a rotating colored sequence position indicator dial marked with standardized symbols. If a sequence interruption or safety shutdown occurs, the dial stops at a specific symbol—such as ▲ for start lockout, ▲I for air damper opening faults, P for combustion air pressure failure, or II for flame establishment failure during safety time. System operators can restart the controller following a fault by using the integrated manual lockout reset push button. When internal mechanical drive or switching board failures prevent sequence progression, ABC Industrial Parts provides tested exchange units and repair options to minimize boiler downtime.
Technical Specifications
| Supply voltage | 230 V AC |
| Supply frequency | 50/60 Hz |
| Power consumption | 3.5 VA |
| Contact rating terminal 3 | 5 A |
| Prepurge time (t1) | 66 s |
| Safety time (t2) | 2.5 s |
| Preignition time (t3) | 2.5 s |
| Interval (t4) | 12.5 s |
| Interval (t5) | 2.5 s |
| Postpurge time (t6) | 15 s |
| Ingress protection rating | IP40 |
Diagnostics and Status Indication
The Landis & Gyr LFL1.635 features an integrated rotating colored sequence indicator dial positioned behind a transparent window on the front housing. This visual display rotates in synchronism with the internal mechanical control sequence, enabling technicians to observe burner startup, pre-purge, ignition, and operating phases in real time.
When a system interlock fails or combustion safety limits are breached, the control mechanism halts and locks the indicator dial on a standardized fault symbol. Resetting the device after correcting the failure condition is performed directly through the integrated front panel lockout reset button.
Replacement and Spare Part Considerations
The Landis & Gyr LFL1.635 utilizes a modular plug-in design engineered to mate with standard AGM410011000 and AGM11 base units. Because electrical connections remain permanently wired to the terminal base, replacing a damaged or failed controller requires no field rewiring or module dismantling. This model serves as a direct drop-in replacement for equivalent Siemens BPZ:LFL1.635 units.
Since all sequence timing parameters—such as the 66-second pre-purge (t1) and 2.5-second safety time (t2)—are defined by internal mechanical hardware, replacement units require no software parameterization, firmware flashing, or digital configuration prior to commissioning. Technicians need only verify physical terminal interlocks, ensure compatibility with the installed flame detector (such as QRA2, QRA10, or QRA4.a sensors), and securely seat the module into its base.
Error Codes & Fault Codes
The following error codes may be displayed during operation or diagnostics:
| Code | Name | Description | Possible Cause | Recommended Action |
|---|---|---|---|---|
| Symbol ▲ | Start position lockout / Interruption | Sequence indicator stopped at start symbol ▲. | Control thermostat / pressure switch contact not closed, or fault signal on flame monitoring circuit prior to start command. | Check control circuit inputs, limit switches, and ensure no premature flame signal is present. |
| Symbol ▲I | Air damper opening fault | Control sequence stops during air damper opening phase. | Air damper drive end switch OPEN not reached or faulty position feedback. | Inspect air damper actuator motor, end switch contact, and wiring to terminal 8. |
| Symbol P | Air pressure switch lockout | Lockout occurs and sequence stops at symbol P. | Combustion air pressure switch failed to close at start of pre-purge or opened during purge phase. | Check fan function, air pressure switch calibration, pressure tubes, and switch wiring to terminal 6/14. |
| Symbol ■ | Air damper closing / low-fire position fault | Sequence stops during movement to low-fire / start-load position. | Air damper actuator failed to reach low-fire position switch contact. | Check air damper actuator, low-fire limit switch, and signal to terminal 4. |
| Symbol II | Flame establishment failure during safety time t2 | Lockout occurs during ignition / safety time interval. | No flame established during safety time, defective ignition transformer, blocked gas valve, or faulty flame detector. | Check ignition spark, fuel supply pressure, main fuel solenoid valve function, ionization probe or UV detector placement and cleanliness. |
| Symbol 1 / 2 | Flame signal loss during operating position | Lockout during main stage operation. | Flame failure during normal operation, dirty UV detector lens / faulty probe, low fuel gas pressure. | Check burner combustion quality, flame signal strength, detector cleanliness, and gas inlet pressure. |
Frequently Asked Questions
Does the Landis & Gyr LFL1.635 require software programming before installation?
No. The LFL1.635 operates using hardware-defined electromechanical cam timing, so no software programming, firmware loading, or parameter configuration is necessary when installing a replacement unit.
Which flame detectors are compatible with the LFL1.635 burner control?
The LFL1.635 supports flame monitoring via ionization probes, photocells, and UV flame detectors including Siemens and Landis & Gyr QRA2, QRA10, and QRA4.a models.
What mounting base does the LFL1.635 plug-in controller use?
The controller plugs directly into standard AGM410011000 and AGM11 base units, allowing unit swap-outs without altering base wiring.
How do field technicians diagnose lockouts on the LFL1.635?
Diagnostics are indicated by a rotating visual sequence dial visible through the front window. The dial stops on standardized symbols (such as ▲, ▲I, P, ■, or II) to identify specific fault conditions.
Is the Siemens BPZ:LFL1.635 compatible with the Landis & Gyr LFL1.635?
Yes, the Landis & Gyr LFL1.635 serves as a direct drop-in replacement for the Siemens BPZ:LFL1.635.
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Specific firmware and hardware versions
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Disclaimer:
We are not an authorised distributor of Landis & Gyr.
Product photos are for illustration purposes only and may differ from the actual product delivered.
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