Siemens LFS1.21A2 Flame Safeguard Controller
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Product Information
The Siemens LFS1.21A2 is an LFS1 family flame safeguard controller for supervising burner flames in gas and oil combustion, boiler, heating and industrial process equipment. It operates from a 230 V AC supply at 50-60 Hz and supports either a Siemens QRA flame detector or an ionization probe. The QRA detector configuration is intended for intermittent burner operation, while the ionization probe configuration supports continuous flame supervision.
When replacing an installed unit, the detector type and burner operating mode must match the LFS1.21A2 configuration. The controller provides one 0-10 V DC analog output for a connected control, indication or monitoring function, together with normally open and normally closed relay contacts for burner control circuits and other system components. Commissioning a spare therefore requires checking the detector, burner sequence, connections and control-panel integration before returning the equipment to service.
The LFS1.21A2 is an active Siemens product and is also a functional replacement for obsolete Siemens/Landis&Gyr LAE10 and LFE10 flame safeguards. For a replacement or repair decision, confirm the exact part number, compatible flame detector, operating mode and required analog and relay interfaces. A tested spare or repair route can support the return of a boiler, burner or industrial heating control panel to operation when the installed flame safeguard has failed.
Technical Specifications
| Manufacturer | Siemens |
| Part number | LFS1.21A2 |
| Model/type | Flame Safeguard |
| Component type | Flame safeguard |
| Product family | LFS1 |
| Supply voltage | 230 V AC |
| Supply frequency | 50-60 Hz |
| Analog outputs | 1 channel |
| Analog output signal | 0-10 V DC |
| Relay contacts | NO and NC |
| Flame detector compatibility | QRA flame detector or ionization probe |
| Operating mode compatibility | QRA detector for intermittent operation; ionization probe for continuous operation |
| Product lifecycle status | Active product |
Communication and System Integration
The LFS1.21A2 integrates with combustion control panels through one 0-10 V DC analog output and normally open and normally closed relay contacts. The analog channel can transmit a flame-related signal to associated control, indication or monitoring equipment, while the relay contacts provide switching functions within the burner control circuit.
Flame supervision is established through a compatible QRA flame detector or ionization probe rather than a programmable automation network. Select the detector according to the burner operating requirement: QRA detection is used for intermittent operation, and ionization probe supervision is used for continuous operation.
Replacement and Spare Part Considerations
For a Siemens LFS1.21A2 replacement, match the exact part number and confirm that the installed burner uses a compatible QRA flame detector or ionization probe. The operating mode must also correspond to the detector arrangement: QRA for intermittent operation or ionization probe for continuous operation. Check that the control panel requires the same 0-10 V DC analog signal and NO/NC relay contact functions.
The LFS1.21A2 provides a functional replacement route for obsolete Siemens/Landis&Gyr LAE10 and LFE10 flame safeguards. Before commissioning a spare, compare the burner sequence, detector arrangement, control-panel connections and required output functions with the existing installation. These checks help identify compatibility issues before the replacement is placed back into service.
Frequently Asked Questions
What is the Siemens LFS1.21A2?
The Siemens LFS1.21A2 is an LFS1 family flame safeguard controller for supervising burner flames in boiler, heating, gas and oil combustion, and industrial process equipment.
Which flame detectors can be used with the LFS1.21A2?
The LFS1.21A2 supports a compatible QRA flame detector or an ionization probe. QRA detection is used for intermittent operation, while an ionization probe supports continuous flame supervision.
What outputs does the LFS1.21A2 provide?
The unit provides one 0-10 V DC analog output, plus normally open and normally closed relay contacts for control-panel and burner control integration.
Can the LFS1.21A2 replace an LAE10 or LFE10 flame safeguard?
The Siemens LFS1.21A2 is a functional replacement for obsolete Siemens/Landis&Gyr LAE10 and LFE10 flame safeguards. The detector type, burner sequence, connections and required outputs must be matched before commissioning.
What should be checked before commissioning an LFS1.21A2 spare?
Confirm the exact part number, supply of 230 V AC at 50-60 Hz, compatible flame detector, intermittent or continuous operating mode, 0-10 V DC analog signal requirement and NO/NC relay contact integration.
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