The sensor detects whether the heater is producing a flame during operation. This information allows the heater’s control system to monitor combustion and shut down the heater when a flame is not detected under the required operating conditions.

Part 251920370000 is also formatted as Eberspächer part number 25.1920.37.0000. It is used with specified Hydronic D4W, D4WS, D4WSC, D5W, D5WS, D5WZ and D5WSC heater configurations.

The sensor is compatible with specified diesel and gasoline Hydronic heaters. It is also used across specified 12V and 24V applications, although compatibility must be confirmed using the heater’s complete identification number.

Flame-sensor replacement requires access to the heater’s internal combustion assembly. Related service components may include the 201820990001 burner and blower gasket set, 252216100000 Hydronic burner, 252121990113 glow-pin lining, 252106011300 12V glow pin and the applicable combustion-air blower.

Always verify the complete heater model, voltage, fuel type and identification number before ordering. Similar Hydronic heater names do not guarantee identical internal components.

Key Features

• Replacement flame sensor
• Monitors flame presence during heater operation
• Designed for compatible Hydronic coolant heaters
• Fits specified D4W and D5W heater families
• Compatible with specified diesel and gasoline heaters
• Used in specified 12V and 24V applications
• Supports heater combustion monitoring
• Helps the control unit identify unsuccessful combustion
• Suitable for heater maintenance, diagnosis and repair
• Genuine Eberspächer/ESPAR replacement component

Specifications

• Part Number: 251920370000
• Formatted Eberspächer Number: 25.1920.37.0000
• Product Type: Flame sensor / flame detector
• Primary Function: Detects flame presence during heater operation
• Heater Type: Fuel-operated coolant heater
• Heater Family: Hydronic
• Compatible Model Families: D4W, D4WS, D4WSC, D5W, D5WS, D5WZ and D5WSC
• Fuel Compatibility: Specified diesel and gasoline heaters
• Voltage Compatibility: Specified 12V and 24V heater configurations
• Installation Location: Internal combustion assembly
• Electrical Connection: Attached cable and terminals
• Brand: Eberspächer/ESPAR
• Condition: New replacement part
• Unit of Measure: Each

Compatible Eberspächer/ESPAR Heaters

Part 251920370000 is identified for compatible versions of:

• Hydronic D4W
• Hydronic D4WS
• Hydronic D4WSC
• Hydronic D5W
• Hydronic D5WS
• Hydronic D5WZ
• Hydronic D5WSC
• Hydronic B4W
• Hydronic B4WSC
• Hydronic B5W
• Hydronic B5WS
• Hydronic B5WSC
• Other Hydronic heaters specifically requiring flame sensor 25.1920.37.0000

Compatibility should be confirmed using the heater identification label and complete heater number before ordering.

This sensor should not be assumed compatible with:

• Airtronic air heaters
• Hydronic S3 heaters
• Hydronic M-II heaters
• Applications requiring flame sensor 251920370100
• Applications requiring a different Eberspächer sensor number
• Heaters that have not been positively identified

Common Service Applications

The flame sensor may require replacement when:

• The heater does not recognize an established flame
• Electrical testing identifies a sensor failure
• The sensor probe is damaged
• The attached cable or terminals are damaged
• The heater repeatedly shuts down after ignition
• The heater records a flame-detection fault
• The burner or combustion assembly is being serviced
• The heater is undergoing a comprehensive rebuild
• Inspection identifies deterioration or contamination
• A technician has diagnosed the flame sensor as the failed component

A shutdown, unsuccessful start or flame-related fault does not automatically confirm sensor failure. The burner, glow pin, fuel system, blower, wiring and control unit should also be inspected during diagnosis.

Important Installation Notes

• Confirm the complete heater model and identification number.
• Confirm the heater voltage and fuel type.
• Verify that the heater requires sensor 251920370000.
• Disconnect electrical power and fuel before service.
• Allow the heater and coolant system to cool before disassembly.
• Inspect the sensor cable, terminals and electrical connections.
• Inspect the burner and combustion chamber for contamination or damage.
• Inspect the glow pin and glow-pin lining while the heater is open.
• Inspect all disturbed gaskets and seals before reassembly.
• Replace damaged, compressed or deteriorated seals.
• Install the sensor in the correct position and orientation.
• Route the sensor cable according to the original heater configuration.
• Keep the cable away from components that could damage its insulation.
• Reassemble the heater according to the applicable service procedures.
• Test heater operation after completing the repair.
• Service should be performed by a technician familiar with fuel-operated coolant heaters.

Related Products

• 201820990001 – Eberspächer/ESPAR Hydronic D4/D5 Burner and Blower Gasket Set
• 252216100000 – Eberspächer/ESPAR Hydronic D4W/D5W Burner
• 252121990113 – Eberspächer/ESPAR Hydronic D4W/D5W Glow-Pin Lining
• 252106011300 – Eberspächer/ESPAR Hydronic D4WSC/D5WSC 12V Glow Pin
• 201819991600 – Eberspächer/ESPAR Hydronic D4WSC/D5WSC 12V Combustion-Air Blower
• 252146991700 – Eberspächer/ESPAR Hydronic D5 24V Combustion-Air Blower
• 2522190123002 – Eberspächer/ESPAR Overheat Sensor with Cable
• 252219250000 – Eberspächer/ESPAR Hydronic D4WSC/D5WSC 12V Water Pump
• 252118250000 – Eberspächer/ESPAR Hydronic D5 24V Coolant Pump
• 225201040011 – Eberspächer/ESPAR Hydronic D5 12V Control Unit
• 225202011001 – Eberspächer/ESPAR Hydronic D5 24V Control Unit
• DH-E2000-MAINT – Eberspächer/ESPAR Hydronic D5 Maintenance Kit