Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Sectioned View of Typical Fuel Fired Booster Heater

Sectioned view of typical fuel fired booster heater

  1. Combustion air fan
  2. Coolant inlet
  3. Coolant outlet
  4. Burner insert
  5. Heat exchanger
  6. Overheat temperature sensor
  7. Exhaust
  8. Fuel inlet
  9. Evaporator
  10. Air inlet


The combustion air fan regulates the flow of air into the FFBH to support combustion of the fuel supplied by the FFBH fuel pump. It is also used to purge and cool the FFBH.


The burner housing contains the burner insert and also incorporates connections for the exhaust pipe, the coolant inlet from the auxiliary coolant pump and the coolant outlet to the vehicle heater.

The burner insert incorporates the fuel combustion chamber, an evaporator and a glow pin and flame sensor. Fuel from the FFBH fuel pump is supplied to a metal mesh, where it evaporates and enters the combustion chamber to mix with air from the combustion air fan. The glow pin and flame sensor provides the ignition source for the fuel-air mixture and, once combustion is established, monitors the flame.


The heat exchanger transfers heat generated by combustion to the coolant.

Two sensors are installed in the heat exchanger casing to provide the control module with inputs of engine coolant temperature. The control module uses the temperature inputs to control system operation.


A canister type muffler is included in the air inlet supply line. The muffler reduces the noise caused by induction roar and acts as a water separator to protect the FFBH in the event of water ingress.


The exhaust pipe and muffler directs exhaust combustion gases to atmosphere below the front right wheel arch. Exhaust vapor may be visible when the FFBH is running, depending on atmospheric conditions.


The Fuel Fired Booster Heater Control Module (FFBHCM) controls and monitors operation of the FFBH system. An internal flow of air from the combustion air-fan ventilates the control module to prevent it from overheating.

The FFBHCM is powered by a permanent feed from the Battery Junction Box (BJB) through the Quiescent Current Control Module (QCCM). The FFBHCM communicates with the Automatic Temperature Control Module (ATCM) over the Local Interconnect Network (LIN) bus.

Auxiliary coolant pump

Auxiliary coolant pump

The auxiliary coolant pump is mounted on the bulkhead panel in the engine compartment and is used to assist coolant flow through the FFBH and the heater core.

The auxiliary coolant pump runs continuously while the FFBH is active.

When the FFBH is inactive, coolant flow is reliant on the engine coolant pump. Operation of the auxiliary coolant pump is controlled by a powerfeed direct from the control module within the FFBH.

Stop/Start System

During a Stop/Start cycle when the engine is shutdown and consequently the engine-driven coolant pump is stationary, the desired set cabin temperature cannot be maintained for a prolonged period, especially in cold ambient temperatures. To counteract this, the FFBH auxiliary electric coolant-pump (when fitted), controlled by the ECM, is used to maintain the coolant flow through the cabin's heater core. This supporting circulation prolongs the set temperature setting in the cabin and accordingly prevents an early engine restart.



The Ambient Air Temperature (AAT) sensor is a Negative Temperature Coefficient (NTC) thermistor, and is mounted in the passenger door mirror.

The sensor is connected to the ECM, which broadcasts an ambient air temperature value over the HS CAN Powertrain bus. This value is received by the Central Junction Box (CJB) over the HS CAN Powertrain bus, and this value is transmitted into the ATCM over the MS CAN Comfort bus, via the GWM.


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