Sorry for not replying, been real busy. It sounds to me like your FBH is faulty.
Basically when the FBH starts, the air fan runs for about 30 seconds to purge any fumes from the combustion chamber, it then idles as it performs self test. It then starts the dose pump at a slow rate, and turns on the glow plug. The air fan will slowly ramp up to full speed, the fuel rate will increase at the same time. The glow plug is turned off, which then functions as a flame sensor, and the FBH ramps up to full speed.
There are several symptoms of a faulty FBH, how long the air fan runs, and the pause between the air fan run time.
Regardless of the type of fault or failure, the FBH is designed to purge the combustion chamber to prevent backfire. This can be from air fan for a second or two > a second or two pause > then air fan for a minute or two. To the air fan just purging for a few minutes.
Problem I am having with Range Rover is its complicated communication with the FBH via its bus and HVAC etc, I still cannot remote start the PCB off the vehicle. I can remote start the FBH using a different PCB, but the Range Rover PCB can only have each circuit tested electronically, in theory this should work, and has on 2 I have done. Thing is, like the Freelander, FBH is under the bloody wheel arch, on a vehicle that can breast stroke. I can refurbish your FBH and repair any PCB component failure.
Several people have approached me about operating the FBH as a stand alone, without being tied to or Range Rover specific PCB, and Range Rover service, . This is easy by using a PCB that can be remote started simply by a earth or 12v signal. The FBH's communication with the vehicles bus system is disconnected at the FBH, and the pins in the 6 pin connector are rearranged. Then remote starting by hard wire, RF, or GSM is simple and cheap. Connecting the FBH to the ATC, involves getting to the power supply wires to the ATC control unit.
Is it just me, or is the Range Rover PCB start up linked to the bus, for people to reach into their pockets up to their elbow when it develops a fault.