Fuel Burning Heater - FBH

sierrafery said:

The FBH controller is part of the unit(nr 9), it's controlled by the vehicle's related electronics via CAN-bus but your vehicle has it only if the VIN is from 581077 onwards (last six digits)

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According to this post, the controller should be part of the FBH as my VIN number is > 581077.

The controller & radio receiver are two separate items.
You need LR036695 & LR030286. There may be supercessions, those are from my old 'extras' worklist
The connector for the receiver should be at the bottom of the 'D' pillar from memory, the antenna cable (second part number) runs up the D pillar and connects onto the antenna printed on the OSR window.

The controller PCBs are part of the FBH. From what I understand, the D1 & D2 were fitted with a CAN bus Themo Top C/Z, remotely started by 12v+ to pin 1, or 12v- to pin 3 using any 12v relay RX/TX module, depending on the PCB.

The D3 & D4 were fitted with a WBUS Thermo Top V that requires a WBUS module to remote start. There are several YouTube videos.

From my experience of my D3, the FBH can only be triggered by a timer module from Webasto, called the oval timer. Or it can be controlled by a remote module available as a kit. There are no factory fitted remotes or timers, but this is obviously for the D3. The D4 will probably be similar though, as the FBH is controlled by a W bus. There is no simple 12v switch line like the thermotop C FBH.

I have to ask what you want the FBH to do? In my experience all it does is warm part of the heater circuit. The heater doesn't function, so the cabin stays cold until you start the engine and give it time to warm up. I also found that the FBH warmed the heater circuit part of the engine nicely, but the moment the engine started, that heat was lost to cold parts of the engine, so kinda making preheating the engine a pointless exercise, especially as the cabin wasn't heated.

The cabin is heated on the D4 - provided it is fitted with the coolant changeover valve, which given the OP doesn't have the timed climate setting on the TSD, is unlikely.
I agree about the 'W bus' on the D3, I've fitted many Webasto 1533 timers, some with a basic remote replicating the 'heat now' button - including on my own D3's, it made a noticeable difference to starting in alpine regions and gave a 'tepid' cabin warmup for a couple of minutes otherwise.
The D4 remote receiver connects to the FBH which then signals the climate control module over MS-CAN, which in turn activates the coolant control valve, heater vents & fan to warm the cabin (or engine, if cold enough) and subject to battery terminal voltage / fuel level.