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Truma Trumatic C 4002 purge fan runs continuously with switch off


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I hope somebody can advise – I have a Truma Trumatic C 4002 (gas only water and air heater) in my Chausson Welcome 85 built in 2005 – 2006. I use the heater very little so am not very familiar with its sounds.


Since immediately after the last CVRT (Irish MOT equivalent) the purge fan runs continuously when there is power to the boiler and the boiler’s rotary switch is in the off position. I suspect that the bouncing of the suspension test caused the issue which I noticed while still at the test centre.


Apart from that the heater runs normally with the exhaust fan running at the normal slow speed in all 4 settings – water 60C, water 40C, heating only and heat and water.


My easy workaround is to remove the dedicated fuse at the 12V distribution board and my plan is to fit a convenient switch in the power line so that the heater has power only when I want to use it and for 2 or 3 minutes after I switch it off to purge the exhaust.


Any advice appreciated as I would prefer to have it working as designed rather than fitting the switch and of course don’t want replace the PCB or rotary switch.



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Welcome to the Out&AboutLive forums.


A Truma Trumatic C-Series C-4002 (image attached below) has two fans.


The green-arrowed combustion/exhaust fan sucks air through a ‘dual tube’ wall-cowl in the motorhome’s exterior bodywork and thence into the gas-burner’s combustion-chamber. The fan then drives the exhaust gasses out of exterior wall-cowl.


The red-arrowed fan sucks air from within the motorhome, forces it over/through the heater’s central heat-exchanger where the air is warmed and circulated around the motorhome’s interior via flexible trunking conected to outlets at the base of the heater.


The later differently-designed Truma “Combi” heaters do have a feature where the combustion/exhaust fan ‘purges’ the gas-burner’s combustion-chamber during the start-up phase and, if a Combi heater is particularly hot inside when switched off, the combustion/exhaust fan will contine to run for a few minutes to cool down the heater’s interior.


However (if I remember correctly from the two Trumatic C heaters I’ve owned) when a C-Series heater is switched off neither of the fans should continue to run. (I can’t see anything in the C-4002 Operating Instructions to suggest otherwise.)




Your C-4002’s combustion/exhaust fan should not be running continuously after the heater has been switched off. Obviously something is amiss and that something might be quite simple and cheap to fix, but it would need investigation to identify the cause of the problem.


There should be no need for you to ‘purge’ the exhaust after the heater is shut down, but it shouldn’t do any harm!


(If you don’t want to pay for professional attention or replacement parts, fit the extra switch.)


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This French advert is for a 2006 Chausson Welcome 85




and the photos suggest that the Truma Trumatic C-Series heater is located under the foot of the bed with a hinged cover above it and with the rotary control-switch on the side of the bed’s base. (1st Image attached below)


If access is possible, you might try removing the heater’s PCB and putting it back in place (or try just waggling the PCB about to make sure it is properly seated in its mount) to see if that does any good. You could also try disconnecting/reconnecting the rotary control-switch and disconnecting/reconnecting all the electrical connections of the cables that attach to the heater. Assuming that your heater did not exhibit the continuous-fan-running behaviour before the CVRT and only began to do this after the vehicle had been bounced about, the problem might be due to the PCB (or a cable connection) having slightly ‘loosened’.


An in-depth article on trouble-shooting a Truma Trumatic C-3402 appliance (very similar to your C-4000) can be found here




and I’ve copied the PCB-related photos as the 2nd and 3rd images below.




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Thanks Derek for both detailed replies - I tried to remove the rotary switch cable connector from the PCB but it is firm and I don't want to use force. I was able to remove the small cover over the PCB connector but not the main cover over the PCB. I think I need to remove the 2 screws visible in your photo and then prise the cover off. I’ll try that but don’t expect to find anything to fix on the PCB. I will probably fit the switch on the supply line.


On your first reply, I expect the 'professional' would want to swap components and I could end up paying handsomely for a PCB and switch. The only habitation service I needed was to the fridge which would stop occasionally when on gas - the first professional said I needed to replace the fridge, the second professional damaged the connection to the gas cylinder but did resolve the problem by cleaning the burner and getting me to change from butane to propane. I prefer DIY whenever possible.




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This 2015 forum discussion includes the suggestion that, in the event of a Trumatic C heater problem, disconnecting everything that can be disconnected and then reconnecting MIGHT do some good.




Truma advise in their Trumatic C installation instructions that the heater should be fitted so that maintenance (and simple repairs) is practicable, but many motorhome manufacturers ignore this completely.


I recall my first Trumatic C heater (a C-3402) stopping working in France on Day 2 of a 10-day holiday in March. I managed to access the PCB and reseated it (I think, as you say, 2 screws need to be undone to allow the cover to be removed - that’s if one can actually get at the cover and there’s room to remove it!) In fact, in my case, subsequent investigation revealed that the insulation on the heater’s gas igniters had fractured, so there was no way the heater would work until the igniters had been replaced.


The asking-price of a C-4002 PCB seems to be at least £400, so - if you can tolerate the fan-running phenomenon and address it successfuly via your extra-switch ploy - that would make good financial sense.

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