Fuel Burning Heater

Nodge68 said:

...It will use approximately 1/2 a litre of diesel per hour. But will stop using fuel, when the engine temperature exceeds 75°C. The FBH internal fan will continue to run however.

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Just a quick question on this, if I may, please? I know the ambient air temperature sensor must be faulty on mine. The FBH comes on whenever the ambient temperature drops below 10 degrees, rather than 5. However, the 75 degree upper limit is of interest. I've replaced my thermostat about 5000 miles ago and it appears to be working fine. Gauge is in the middle, heater works fine and the car warms up really quickly. It's not the Renault thermostat, (I didn't know about that trick when I fitted it!) it's a Circoli replacement.

The car takes about 3 or 4 miles to warm up, but even if I drive it 10 miles, the FBH still seems to be running when I come to a stop - long after the coolant must have reached 75 degrees (I'm guessing)? I note your point about the internal fan continuing to run, and it's true that at the end of 10 miles, the exhaust tube of the FBH is only lukewarm so I know it has stopped burning fuel, but it does seem like a long time for the fan to continue to run? How does the FBH sense coolant temperature? Does it have its own sensor, or does it use the engine's coolant temperature sensor? Does the engine have more than one sensor? (i.e. one for the gauge and one for the engine management system)?

Avocet1 said:

Just a quick question on this, if I may, please? I know the ambient air temperature sensor must be faulty on mine. The FBH comes on whenever the ambient temperature drops below 10 degrees, rather than 5. However, the 75 degree upper limit is of interest. I've replaced my thermostat about 5000 miles ago and it appears to be working fine. Gauge is in the middle, heater works fine and the car warms up really quickly. It's not the Renault thermostat, (I didn't know about that trick when I fitted it!) it's a Circoli replacement.

The car takes about 3 or 4 miles to warm up, but even if I drive it 10 miles, the FBH still seems to be running when I come to a stop - long after the coolant must have reached 75 degrees (I'm guessing)? I note your point about the internal fan continuing to run, and it's true that at the end of 10 miles, the exhaust tube of the FBH is only lukewarm so I know it has stopped burning fuel, but it does seem like a long time for the fan to continue to run?

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The burner shuts off when the temperature of the heat exchanger gets over 75°C. However the fan continues to run in readiness for the next firing cycle, if it's still getting the run signal from the external temperature sensor. So it can appear that the FBH is running, however it's only drawing air through, and not burning fuel and making heat.

Very Interesting replies all,
and TBH I`ve done nothing to check or remedy the fault except plugged in my "cheap" OBD2 code reader that told me nothing untoward is / has happened.
I will Investigate further at a later date now, as its still a bit cold for this old boys bones to be outside
and under ? my much loved Hippo.
But, researching a problems always is helpful when reading your comments, so, Thank you all.

Nodge68 said:

The burner shuts off when the temperature of the heat exchanger gets over 75°C. However the fan continues to run in readiness for the next firing cycle, if it's still getting the run signal from the external temperature sensor. So it can appear that the FBH is running, however it's only drawing air through, and not burning fuel and making heat.

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Thanks Nodge. So the FBH has its own internal sensor for water temperature, somewhere in its heat exchanger then?

And thanks that makes sense. The FBH exhaust isn't very hot after 10 miles, so I guess it is just the fan that's running. I'll have to have a look at that....

...when the weather's warmer! Oh...er...hang on...

Last question, does the front bumper definitely have to come off to change the sensor?

Avocet1 said:

Thanks Nodge. So the FBH has its own internal sensor for water temperature, somewhere in its heat exchanger then?

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Yes that's correct. The FBH ECU then controls the burner output, based on the temperature of the FBH water jacket temperature sensor. It has 3 stages of firing the burner, which are controlled by the FBH ECU, depending on temperature and output needed. But basically it'll run at full power, half power or fan only.

Avocet1 said:

Last question, does the front bumper definitely have to come off to change the sensor?

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Unfortunately it does, and to be honest, if you're taking the bumper off, you might as well give the FBH combustion chamber a clean too. I replace the bumper screws with stainless steel items at the same time.

Excellent advice, as always! Not really looking forward to trying to get the front bumper off, to be honest. 18 years is a long time!

From switch on, it takes a Thermo Top 2 minutes to get up to full operating speed. From switch off, it takes 2 minutes to shut down.
When the heat exchanger reaches 78°C it ramps down to idle, it will not ramp up again until the heat exchanger drops below 58°C.
The FBH temperature sensor protrudes from the PCB, and rests on a pad on the heat exchanger body.
Pic of me replacing one.

The first thing I do with any motor of mine with a FBH, Is get rid of the ambient temperature start stop function. I like it to start and stop when I want. Only good thing about it, is it will shut down if the alternator stops working.
Unplug the 2 pin plug first, and plug 2 pin plug in last (wrong order can damage the PCB).
At the 6 pin connector
Populate pin 1 and send the wire up to the engine bay fuse box for later use.
Cut the temp sensor Pin 3 wire a few inches from the plug.

Connect a wire to the end going to the plug, tape the end going to the loom. Run the pin 3 wire into the cabin.
Find a suitable permanent 12v fuse, and pop a piggy back in it.
Connect the wires to a switch.
When the engine is started and the FBH is wanted...Just switch it on, when the engine is warm enough, switch it off.
If the FBH is wanted to pre warm the heater matrix, switch it on. Or connect a simple 1ch Rx/Tx into the engine bay fusebox.

Devilish said:

From switch on, it takes a Thermo Top 2 minutes to get up to full operating speed. From switch off, it takes 2 minutes to shut down.
When the heat exchanger reaches 78°C it ramps down to idle, it will not ramp up again until the heat exchanger drops below 58°C.
The FBH temperature sensor protrudes from the PCB, and rests on a pad on the heat exchanger body.
Pic of me replacing one.

The first thing I do with any motor of mine with a FBH, Is get rid of the ambient temperature start stop function. I like it to start and stop when I want. Only good thing about it, is it will shut down if the alternator stops working.
Unplug the 2 pin plug first, and plug 2 pin plug in last (wrong order can damage the PCB).
At the 6 pin connector
Populate pin 1 and send the wire up to the engine bay fuse box for later use.
Cut the temp sensor Pin 3 wire a few inches from the plug.

Connect a wire to the end going to the plug, tape the end going to the loom. Run the pin 3 wire into the cabin.
Find a suitable permanent 12v fuse, and pop a piggy back in it.
Connect the wires to a switch.
When the engine is started and the FBH is wanted...Just switch it on, when the engine is warm enough, switch it off.
If the FBH is wanted to pre warm the heater matrix, switch it on. Or connect a simple 1ch Rx/Tx into the engine bay fusebox.

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Brilliant, thanks! I assume the advantage of doing it that way, is that when you manually switch it off, it still goes through its cool-down cycle so it doesn't "cook" anything?

Thanks all.
bye the bye, I did buy not 1 but 2 of them RX/TX units from the world of Bay,
there still in the packaging, actually almost looking at me so I cant forget I got them.
lol
When It gets warmer then..
(but silly me, i wont need them then)
Oh well.
press on..
have a great evening all.
Ian.

I had my FBH on remote control for a couple of winters. I wired it so when the HBH was hot, the interior fan started up to warm or de-ice the cabin before I got in.

This was lovely, getting into a warm car was vary pleasant on a cold morning.

However it came with an unexpected issue. The car was very difficult to start. The engine was close to running temperature so no glow plugs. However the fuel and air going in were cold, which seemed to confuse the EDC. This made starting the car very difficult indeed. It simply wouldn't fire, unless I started the engine with the throttle fully down, and only then with a lot of cranking. Maybe it was an issue with my particular TD4, but it made starting with the pre-heater so difficult, I removed the system. I've actually pinched my FBH so I can heat the wife's hot tub using kerosene, instead of electric.

Nodge68 said:

I had my FBH on remote control for a couple of winters. I wired it so when the HBH was hot, the interior fan started up to warm or de-ice the cabin before I got in.

This was lovely, getting into a warm car was vary pleasant on a cold morning.

However it came with an unexpected issue. The car was very difficult to start. The engine was close to running temperature so no glow plugs. However the fuel and air going in were cold, which seemed to confuse the EDC. This made starting the car very difficult indeed. It simply wouldn't fire, unless I started the engine with the throttle fully down, and only then with a lot of cranking. Maybe it was an issue with my particular TD4, but it made starting with the pre-heater so difficult, I removed the system. I've actually pinched my FBH so I can heat the wife's hot tub using kerosene, instead of electric.

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Oh, thanks for that Nodge68.
as In my avatar, my hippo is lost under my quite large carport I built originally for my D1 I had, but, it does keep most of the elements of the car including falling frost. The colder It got this winter the more "stuff" I took out the end of the car port as to drive further in for more weather protection.
It was worth the hassle building it a few years ago now.
Originally I was going to do a similar thing to yours thus 2 RX/TX units, but am holding back on that Idea, maybe either ? buy a new behind grill thermo switch, or put a switch in the fesed feed ? to control the on/off more ?
Currently, in the coldest weather, my FBH is not working, but on my list of must do`s.
Just another thing, like your crazy hot tub Idea.
And, my son, being a VW camper van nut, Is buying one of them Chinese FBH to put in his van, after reading so many good reports about them... They seem to start around £100 or so...
more on this as I know it.

Avocet1 said:

Brilliant, thanks! I assume the advantage of doing it that way, is that when you manually switch it off, it still goes through its cool-down cycle so it doesn't "cook" anything?

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Correct.
Another advantage of severing the temp sensor, and fitting a switch. If you are only moving the vehicle off the drive, moving it forward to open garage doors, or your journey is only a minute or so, but it is ****ing down or snowing, having the FBH switch itself on is a bloody waste of time. Once the FBH has been accessed, and wires put up into the engine bay, Installing a rx/tx takes about 10 mins, and it fits inside the fuse box. This can be used just like a switch, turn the FBH on/off at your pleasure. Switch on 5 - 10 mins before you start up, switch off when cabin heater is warm enough, or leave it on, the FBH will control itself. This time of year, if I switch on 5-10 mins before starting, after 5 mins driving it is not needed and I switch it off. If I switch on after I start the engine, after 10 mins mins driving it is not needed.

I also hooked it up to the A/C, installed a GSM unit, so she can start it by text, the A/C switches itself on after 5 mins. In summer when it is so hot the steering wheel burns your back, hands, and your sunglasses burn the bridge of your nose. she can send a text to turn the A/C on.

From what I understand, the Freelander BCU has no lazy locking/venting feature. Baffled as I believe the Freelander is a MG Rover design. A favourite mod of mine is remote controlling the windows & sunroof when it is baking hot. Or you lock the vehicle, to notice all the windows are not closed. I have acquired a tx that reverses the NO & NC polarity, I intend to fit into the drivers door.

Thing is, the Freelander belongs to the wife, she does/will not know how to work any of it.

Nodge68 said:

However it came with an unexpected issue.

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Spurious issues such as this and a plethora of other weird electrical issues, I found common, especially with MG Rover.
Freelander FBH has a analogue PCB, it is started with 12v from sensor to pin 3, or remote by 12v to pin 1.
I know you know this already Nodge, may be interesting for others.

Pin 2 is for BUS communication, FBH PCB on RR L322, Audi, BMW etc, (Disco has a thermo Top V, also digital, and the fuel is delivered by a venturi, instead of a diffuser) are digital, and will ONLY start up if pin 2 is communicating with the vehicle. the FBH has to be woke up by pin 2 first, then it will start if pin 2 is in constant communication with the FBH. Some digital PCBs require a run command pulse signal to pin 2 every 15 seconds, if this signal stops, the FBH shuts down.

Two types of PCB factory fitted to Freelander and MG Rover, lets call them Freelander & MG Rover type, One type is always fitted to Freelander FBH, because pin 1 & pin 3 are transposed, Freelander PCB accepts 12v command from pins 1 & 3. MG Rover type accepts 12v command to pin 1, but earth command to pin 3. If buying one, going by model and/or serial number is a waste of time, my guess is, at least 75% do not have the original PCB, I have serviced and repaired hundreds, have had up to 20 MG Rover type apart at the same time, doubt if any PCB went back into the FBH it came from. The FBH however, when re assembled, if a PCB is fitted, the FBH is clearly marked L322, BMW, Rover etc.


Because the BUS was never fully developed on the analogue PCB, on many vehicles such as Freelander, and MG Rover, pin 2 causes havoc with the vehicle BUS, many that made no sense whatsoever
On the analogue PCB used on Freelander and MG Rover, the only thing pin 2 is used for is Thermis Test diagnosis, and even then, some PCB's will not communicate with Thermis Test.

To prevent and cure any FBH Bermuda triangle problems, look at my 6 pin connector pic, and cut the Pin 2 BUS wire. This pin has absolutely nothing to do with FBH operation. Every Freelander I have worked on, or fitted a FBH to, I cut pin 2. Will stop/stops every FBH Bermuda triangle issue. I also take RX/GSM supply direct from the battery.

As Nodge has already mentioned, pin 4 will supply power when the FBH reaches I forgot °C, this should only be used to switch a relay, and not to power A/C motor direct.

A MG Rover PC can be used on a Freelander, as long as there is no remote control, if there is then pins 1 & 3 need transposing, and the remote signal changing from 12v to earth.

Buy a Thermo Top taken from any motor I mentioned above, and although identical to look at, (even the PCB) , The FBH itself is no different, but the PCB will NOT work on a Freelander.

Anyone who wants to come to mi casa, and start a RR L322, Audi A7, Disco V, or BMW E39 FBH on my test bench, (using their own interface) can have a fully refurbished FBH for free, will even throw in a rx, fobs, and a GSM unit.

will add some pics later

PCB identification. As already mentioned, PCB on L322, BMW, MG Rover, are identical, the only difference is the IC software, and it is read only, so no converting a digital PCB to analogue.
Freelander PCB easily identified by the caps being mounted next to each other.
I have seen them for sale said to be from a vehicle I knew damn well it was not taken from.








A problem with buying a used FBH, some sellers switch on, the air fan starts up, and the FBH is thought to be working.

Regardless of any start up faults, when the FBH receives a start up command, the air fan starts and purges the combustion chamber. The FBH then goes through a self test start up protocol. Any faults detected by the PCB during start up, the FBH shuts off, and the air fan purges the combustion chamber. If there is no response from a Freelander FBH, this is rare, but it is sign it has been submerged, and would make a good door stop.

Pics of one of several Freelander PCB's I had for repair. Yeh, right. (not Yeh right, that will take some fixing, but Yeh right, oi missus, does this go in the blue bin or the green bin)

Testing the dose pump.
Disconnect the fuel line from the FBH.
Unplug, 2 pin plug, THEN 6 pin plug.


A stopwatch and same ambient temperature would be needed to tell the difference between 11-13 ml per minute. Just below 10ml per minute, is ok if satisfied with how fast the FBH gets up to temperature.
A Thermo Top will start and run if the dose pump pulses 5ml per minute. I tried a 2Kw pump on my test bench, got fed up of waiting for it to get hot enough to ramp down.
Ah well enough rabitting from me.

Ian burritt said:

my son, being a VW camper van nut, Is buying one of them Chinese FBH to put in his van, after reading so many good reports about them... They seem to start around £100 or so...
more on this as I know it.

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For what it is worth.
Eberspacher Airtronic. Webasto Airtop £500+, or a £100+ ish version with any other brand name. I would buy a used WORKING Eb or Web, decoke it, clean out the venturi, fit a new glow plug. Sorted. I am not saying cheap ones are crap, I do not know enough about them, but I have had 2 people approach me with faulty Cheap units, one out of the box. I do know air type FBH's, are not subject to the finishing procedure, that contributes to the thermo top PCB component failure
Web and Eb heat exchangers are not bought from the same factory as cheap units. there is a clear, and IMO superior difference.

FBH identification. Parking/auxiliary - auxiliary only function.

A thermo Top fitted for use as a auxiliary heater, has no on board water pump (most A7's and E39's). Because the water pump has to pass the PCB current draw test during start up, a emulator is connected to the water pump socket, or a blanking resistor plug on factory installations, as seen in the pic below. So if a Thermo Top has a 2 pin single wire plug in the water pump socket, a blanking plug, or the socket is clean as a whistle, the FBH PCB is almost certainly BMW


If a FBH is only wanted as a auxiliary heater, without a water pump, all that is needed, is for the FBH to think a good water pump is fitted. The easiest way to do this is to connect a 21W bulb to the water pump socket.
If a Thermo Top has a PCB that looks like the one below, then it is a Audi PCB.

Devilish said:

For what it is worth.
Eberspacher Airtronic. Webasto Airtop £500+, or a £100+ ish version with any other brand name. I would buy a used WORKING Eb or Web, decoke it, clean out the venturi, fit a new glow plug. Sorted. I am not saying cheap ones are crap, I do not know enough about them, but I have had 2 people approach me with faulty Cheap units, one out of the box. I do know air type FBH's, are not subject to the finishing procedure, that contributes to the thermo top PCB component failure
Web and Eb heat exchangers are not bought from the same factory as cheap units. there is a clear, and IMO superior difference.

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Thanks for that info Devilish.
I can only comment on what my son tells me, then its only what he reads of others,
so wondering if one gets bad results would we read about it/
Hey Ho, anyway, when the "Lad" (hes 50) gets one and I get roped into fitting it, maybe an update in the future.
life eh..
lol