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At the risk of turning the forum into a clinic for owners of cdts with defective fbh's,some ideas on this would be appreciated.Have had the 75 for just over a week.The first time I drove it I pulled over to see what the "whirring" noise coming from the battery area was.At first I thought it was the fuel pump until I realised that it has an fbh (Webasto thermotop Z/C-D to be exact.)

It was making plenty of noise,but not actually igniting.After spending a while on the forum I have discovered that these things are notoriously unreliable!To cut a long story short the fbh tries to operate intermittently even when the car is locked (is it not supposed to be fed via the ignition?).It does not have a timer or remote,so I am guessing that it is temperature controlled (puzzling since it was about +10 degrees outside?)I have checked the fbh fuel pump and this does not attempt to operate when the heater makes a noise.I would really like to get this beast working if possible,as we would find it really useful (live in the sticks, car lives outside)
 

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rover_75_tourer
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Since it may be functioning as a parking heater, it won't be wired through the ignition - with that function, it's supposed to be started remotely without entering the car.
The noise could be the air fan or circulating pump. As you say, it shouldn't be operating under those conditions. I'd check the connections for shorts or corrosion. Previous posts have described how the heater can be tested by grounding one of the pins, so maybe this is happening by chance.
 

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After 3 attempts it will lock-out. The general advice is to pull the 2 pin plug for 10 seconds to reset it. There have been a spate of failed FBH's but I think it is people doing this reset rather than an inherent design or quality failing. Somewhere I read you should remove the 6 pin plug first, then the 2 pin so the PCB does not get damaged.

I'd suggest a reset, but also check to see if you get a pulsed voltage to the pump.

As for why it started in the first place .. . . there are a few posts on the subject but can;t recall the out come. Typical checks would be plenum drains and battery .


any takers?
 

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rover_75
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Hi,
as stated there are several threads on this subject ,but several opinions were that it required somebody brave enough to 'donate' a known working FBH control panel to someone with a 'faulty' FBH. This would prove if the fault was
infact on the FBH board ,or something else .( JohnFol I think origonally suggested a possible 'swap' scheme ),but I never heard if it had ever been done.
 

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rover_75_tourer
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Hi folks. This is my first posting, and it's to report success today (I hope!) with the FBH problem on my 51-plated CDT Tourer.

The FBH had exhibited the common symptoms. 1) Main fan on full speed whenever the ignition was on; you could easily tell when the car was about to arrive home because the noise of the fan could be heard half a mile away! 2) FBH intake fan making a couple of abortive attempts to fire up whenever the remote was used. 3) The same fan cutting in and out seemingly at random, even when parked (my wife described the problem as "the pigeon under the bonnet"). Whenever we came back from a holiday, the battery was flat - neighbours had apparently heard that pigeon during the first half of our absence, but then it stopped (presumably because the battery was, by then, flat).

I'd tried replacing the fuel pump; I'd re-primed the fuel lines by pulsing 12v to the pump until it spat fuel from the FBH end of the line. Still no luck. As a temporary measure, I pulled fuse no. 8 from the engine fuse-box, and left it out. At least that cured the pigeons, if not the main fan problem!

Previous postings here pointed to the Webasto PCB as the likely cause of the problem, and that replacements were unobtainable here. I therefore established a watching brief on the German eBay site, where I eventually found a replacement PCB offered - see eBay item 280121611432. I put it in this evening, and immediatly, that main cooling fan has stopped running full belt all the time, only cutting in when needed by the aircon.

I have yet to test that the FBH now actually works by faking a "Blimey it's cold" signal from the air temperature sensor; I hope to do that later this week and report back here.

The PCB was listed as a Steuergerät Platine Webasto Thermo Top C Standheizung (=Control PCB for Webasto Thermo Top C Heating). It cost me about £50 including postage. I have spotted another German eBayer who occasionally offers reconditioned Webasto PCBs at a "Buy it Now" price of 99 Euros, but he doesn't seem to have offered any for the past month.

I'll keep you folk updated with the results of the temp sensor test. If someone wants to buy one of the reconditioned PCBs, and you don't speak German let me know, and I'll keep an eye out for one.

Meanwhile, if any of the techies on the forum would like to have a look at my old PCB to see if there's anything that can be learned for the benefit of other people with the same problem, feel free to contact me!
 

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Hi folks.
Meanwhile, if any of the techies on the forum would like to have a look at my old PCB to see if there's anything that can be learned for the benefit of other people with the same problem, feel free to contact me!
Yes I would be more than interested in looking at the PCB, as I have the electronic rescources to investigate the problems.
Will PM you with details.
Rgds
Colin
 

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Hi Colin, I'd be interested in any solution. I did get 1 response where a guy who had the non-pulsing fuel pump found that cleaning the combustion chamber solved the problem.
 
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