# Truma thermostat



## cynigy (Mar 19, 2007)

Has anyone else experienced thermostat "drift" on their Truma C6002?
Sometimes it is impossible to set the thermostat low enough to maintain a comfortable level of heating overnight, ie it is on all the time, making the 'van uncomfortably warm for sleeping. The only alternative seems to be to switch off the heating altogether, thus running the risk of the dump valve operating.
The problem seems to occur less frequently when on electric hook-up, but otherwise seems completely random. Any suggestions gratefully received!


----------



## iconnor (Nov 27, 2007)

Never experienced that problem. If on hook up I turn the electric water heating on and the blown air heating off, then plug in a small oil filled electric radiator to maintain some background heat.


----------



## gromett (May 9, 2005)

I have the same problem on both my current Eura and on my previous hymer. The thermostat on the Traumas are pretty useless in my opinion.

It is on my list for stuff to look at.

Karl


----------



## JeanLuc (Jan 13, 2007)

The C6002 in our van works fine, but the fan seems to be pushing out air very gently for a lot of the time when the stat is set to low. The boiler cuts in and out from time to time during the night so I think everything is working correctly. On cold nights, we run the stat at setting 1 or 2.

Just a thought - is the temperature sensor in a location that is subject to cold draughts? E.g. near a vent or window that you leave open to prevent condensation? If so, that could cause the system to keep running even when the main part of the van is warm enough.


----------



## maddie (Jan 4, 2006)

Hi it could be where the thermostat is located ie low down?
terry


----------



## Roger7webster (Oct 10, 2006)

The stat looks like a small black mushroom head about 25mm diameter
Located on the underside of the over cab bed on some A class m/homes


----------



## maddie (Jan 4, 2006)

Roger7webster said:


> The stat looks like a small black mushroom head about 25mm diameter
> Located on the underside of the over cab bed on some A class m/homes


IF that's the case it could be that it is always cold in the front of the cab,making it work all the time.
When on hook up is the heater just not as hot as on gas? there by not being as uncomfortable?
terry


----------



## pippin (Nov 15, 2007)

We find that there is a very wide hysteresis curve with our Truma thermostat.

In laymans terms it means that the heating cycles on and off between quite hot and quite cold.

Also, it is very fiddly trying to turn the dial to an exact setting.

It is something to which I will be applying my electronic brain before too long.

Err, it's not my brain that is electronic - actually I 'spose it is really!


----------



## jhelm (Feb 9, 2008)

JeanLuc said:


> The C6002 in our van works fine, but the fan seems to be pushing out air very gently for a lot of the time when the stat is set to low. The boiler cuts in and out from time to time during the night so I think everything is working correctly. On cold nights, we run the stat at setting 1 or 2.
> 
> Just a thought - is the temperature sensor in a location that is subject to cold draughts? E.g. near a vent or window that you leave open to prevent condensation? If so, that could cause the system to keep running even when the main part of the van is warm enough.


I recently checked the owner's manual to discover that the fan has two speeds. If the temperature is close to the desired one the fan is on the low setting. A very nice feature actually.


----------



## UncleNorm (May 1, 2005)

Pippin explained:



> _*We find that there is a very wide hysteresis curve with our Truma thermostat.
> 
> In laymans terms it means that the heating cycles on and off between quite hot and quite cold. *_


That's why I keep advocating the plug-in thermostat 'ET05' with its hysteresis curve of 0.1°C. During a winter day, it is set at say 20°C. When the temp drops to 19.9, the heater will come on and take it back to 20.0. At night time, we might set it at 12C. If the temp drops to 11.9... You get the picture! :wink:

We have used ours with a fan heater and now it's in use with an oil-filled 900w heater. It is so easy to set up and extremely precise.


----------



## gromett (May 9, 2005)

UncleNorm said:


> That's why I keep advocating the plug-in thermostat 'ET05' with its hysteresis curve of 0.1°C. During a winter day, it is set at say 20°C. When the temp drops to 19.9, the heater will come on and take it back to 20.0. At night time, we might set it at 12C. If the temp drops to 11.9... You get the picture! :wink:


The constant switching on and off would drive me up the wall :?

I think a 2C spread would be ok. Mine seems to have a mind of it's own 
Wish they would mark the dial in DegreeC instead of 1-9 or whatever it is.

Karl


----------



## UncleNorm (May 1, 2005)

Hi Karl!



> _*The constant switching on and off would drive me up the wall *_


Don't hear a thing! :wink: #Silence is golden...# :roll:


----------



## cynigy (Mar 19, 2007)

Thanks to all who have replied so far, some useful advice there, but we're still waiting for the one that says, "Yeah, we had that, and it turned out to be so-and-so."
Perhaps I should have pointed out that we've been full-timing in this 'van for about 4 years now, and this is the first time we've had a problem with the thermostat.
I should also point out that I posted this topic in the Hymer section by mistake - obviously it's not a Hymer-specific problem.

Thanks again, and keep 'em coming.

Nigel


----------



## bodgerco (May 23, 2005)

In the Truma handbook for the later model it says that if the thermostat is open circuit then the boiler runs without control - ie flat out. This happened to me and the thermostat was , indeed, broken. I wonder whether, in your case, the one lead, either at the thermostat end or the boiler end, is intermittent. 


Roy


----------



## cynigy (Mar 19, 2007)

Thanks for that, Roy. I have tried jiggling the thermostat lead at the boiler end, with no effect. I'll try and find a way in to the actual sensor, to see if there's anything untoward there. I've managed to unclip the plastic cover, exposing the thermistor itself (if that's what it is), but was reluctant to start tugging at it in case I broke something and made things worse. I'll see if I can find a way in to the panel it's mounted on, and take it from there.

Nigel


----------



## pippin (Nov 15, 2007)

OK - just been out to our van to do some research for you.

I removed the Hymer control panel so that I could get to the rear of the sensor unit to push it out.
If I had pulled hard enough it might have come out anyway.
It is held in place by plastic clips that would be unlikely to break if you did try to force it out, but I was worried about my finger nails!

I was expecting to find a PT100 sensor but, no, it is a bead thermistor.

It has a gold tip, orange body and a black ring but the colours are not easy to discern and I have not yet been able to identify it.
Will need another look using a magnifying glass.
These things are only pence to buy. (sensors, not magnifying glasses -silly!)

Disconnecting it brings the heating full on.

Its open circuit resistance at 15C is approx 10K and the resistance falls as it is warmed up.

The open circuit voltage on the disconnected supply leads is 8V which falls to 5.5V when the thermistor is reconnected at approx 15C.

The wires do not go to the adjacent Truma dials/switches but appear to be a separate pair that go all the way to the boiler. 

The thermistor is probably just crimped into the holder and therein could lie the problem.

I didn't want to firkle around too much in case I messed things up and right now we need the heating to be OK!!

I will let you know when I identify the thermistor accurately.

Much better for it to be at the sensor end than to have a problem on the boiler control panel!


----------



## pippin (Nov 15, 2007)

Update:

The colour code may be Gold tip, Orange ring, Black ring and perhaps Brown body.

The thing is so tiny that it is difficult to be sure.

Have a look on the Maplin website as there are a few thermistors on there.

I could not find the exact clour coding though.

I would still suspect poor crimping of the thermistor leads into its holder.


----------



## Pudsey_Bear (Sep 25, 2008)

UncleNorm said:


> That's why I keep advocating the plug-in thermostat 'ET05' with its hysteresis curve of 0.1°C.


Where can we get one from at sensible money.


----------



## carol (May 9, 2005)

UncleNorm - I must be thick tonight, not unusual, but where would you plug in a thermostat ET05 on a Truma?

Carol


----------



## UncleNorm (May 1, 2005)

Hi Kev and Carol!

Kev, please try this link:

http://www.tlc-direct.co.uk/Product...ords&kw=et05&gclid=CPPgzaWqy5gCFYFA3godi27J1A

Carol, sorry if I misled you! :roll: The ET05 plug-in thermostat plugs into the mains side of the MH. Then a fan heater or oil-filled heater is plug into IT. It's more of a back-up system for keeping the MH warm. TOTALLY USELESS IF NOT ON MAINS HOOK-UP! :roll: :wink: :lol:


----------



## carol (May 9, 2005)

That's why I was confused - I had that bookmarked already as a friend had told me about them, but that would be OK for home here, but at the end of the day, we don't have hook-up when away, so only use gas, and like others, find the truma is inconsistent with its temperatures...

Carol


----------



## bodgerco (May 23, 2005)

Carol

We also find the Truma temperature control inconsistent - it must be a 'feature'.

Recently our Truma - the new type - blew up completely resulting in a trip to Truma UK for a complete replacement. As an aside I found them absolutely brilliant, however, a couple of things which I learned there are important I think.

The thermister ( the black thingy) should be on a vertical surface not , as in our case, on a horizontal surface. We cannot control that because it is down the the design.

The other vital thing is the recirculating air vents. Because the heater heats air to heat the van, it must then take that same air back from the van in order to heat it further. This recirculating air is important. It would be possible to heat air from outside but that doesn't make sense since the temperature into the boiler would always be the same - cold - so the Truma would only be able to lift it's temperature by a certain amount and during winter this would not be adequate when the outside temp is very low. So the Truma Combi systems use the air it has already heated to reheat it further and this requires that that air be recirculated.

If there is little or no recirculating air then the input fan on the boiler runs too fast trying to suck air in , which is finding it difficult to do. In our case it effectively burned out due to the lack of recirc air. Again fundamental design issue.

On many vans where the Truma is located under a bed say, then the necessary recirc air is easily established in the gaps between the bed and the base, but when it is located in a wardrobe or a kitchen unit - as is yours and ours, then the recirc air becomes more crucial. Truma quote 150 Sq Cm of gap is required to achieve the necessary recirc air volume. 
In our case I have now added the necessary vents. In your van I recall the vents are in the worktop and I guess that is used for recirc. Against that I think your vents would also be used to allow the heat from the boiler to escape to avoid that area under the kitchen overheating , and getting your drawers too hot - perish the thought. I suspect that since the same vents seem to have a dual function that might make temperature control tricky too.

That just about exhausts my Truma knowledge!!

Roy


----------



## carol (May 9, 2005)

Roy thanks - these things should not have to consume our time so much. As to our thermostat, it is fitted at the top of the doorway, now I will have to check but I think it is horizontal not vertical.... will look when I next go out to van, not now as it is raining and I am watching the rugby....

So off now.

Carol


----------



## pippin (Nov 15, 2007)

Bodgerco/Roy - many thanks for your full account.

On our Hymer I just cannot figure out how the air is recirculated.

The boiler is in the rear garage, under the transverse bed.

There are of course various outlet vents dotted around at low level in the habitation area.

There is even one in the garage!

There is also a very thin outlet pipe that runs straight up from the boiler area and pokes out by the foot end of the mattress. 
It has no open/close vent, just an open end.

The garage area is not totally sealed as light from the garage can be seen around the edges of the bed if the mattress is moved slightly.

When the heating is on, even in the recent freezing conditions, the garage is like a sauna compared with the habitation area.

Lifting the foam rubber mattress up from its base allows a lot of heat to escape from the area. There is a gap between the garage ceiling and the bed slats that gets really hot due to the insulation factor of the foam mattress.

We really want all this heat in the cab/hab area rather than in the garage.

I am tempted to try to install some return flow ducting from the cab area back to the garage, but it would not be an easy job to do.

Any thoughts anyone?


----------



## carol (May 9, 2005)

pippin - it sounds like it needs balancing - I think it was on here a few days ago someone posted how to do it..... search for it, but what I recall was to close all vents, open the vent furthest from the boiler - fully - feel the strength of the air, and then working back towards the boiler, open each vent until you get the same pressure....and I expect your garage one is closest and fully open, hence why so much air and warmth is there....it is worth a try.... will be interested in how you get on

Carol

(If I am wrong, will someone point to the correct post pls)


----------



## pippin (Nov 15, 2007)

Will try the balancing act but in fact the garage one is very firmly closed.

I suppose that I ought to remove as much of the woodwork from around the boiler and visually check that all the output tubes are firmly connected.
There are several output points in different directions.

It is all so difficult to access.


----------



## maddie (Jan 4, 2006)

Hi Pipin the outlet nearest the heater has been left open by the installer because one of the outlets must be ! (so no one can close them all by mistake)The outlets are screwed on and have a flap that can be adjusted.Unscrew the farthest away and replace it with the nearest permanently open one,closing the flap to force the air to come out of the now far open one :lol: Open the others to your preferred opening/heat setting.--the whole cream face unscrews--also check non of the ducting pipes have been squashed.--just as Carol says ---
terry


----------



## cynigy (Mar 19, 2007)

Many thanks Pippin for your detailed research above and beyond the call etc.
Had no time over the weekend to investigate further but this stuff looks promising. Will update as and when.


----------



## bodgerco (May 23, 2005)

Pippin

Don't think of me as the Truma expert I am not but This is what I think is happening.

1. The low level vents you describe are the normal air flow from the boiler into the habitation area - ie pushing air out into the van living area. 

2. The air in the habitation area is constantly monitored for temerature based on the setting of 1-9 or, on the very latest Truma model, 1-5. Inadequate, coarse control but that's how it is.

3. While the sensor detects that the van is colder than you have set on that dial it runs a pump - more a sucker really - which pulls warmed air back from the habitation area into the boiler to be reheated further. This is the recirculating air and the Truma spec says there must be 150sq cm of gaps to enable that and provide sufficient air volume. This gap is a different one from the vents referred to in 1. above.

4. In your case I would have expected that the gap under your transverse bed would have provided perfectly sufficient recirc air.

5. I don't know what the small pipe which you describe going from the garage into the van could be unless Hymer have taken an ultra cautious approach and ensured there is 'some recirc air flow even if that gap under the bed ceased to exist for some reason. 

In my case the Truma is under the L shaped kitchen unit. An oven under the worktop had adequate gaps around it to provide the necessary recirc air for the boiler. However, the oven was changed for a Microwave and the fitter thought how neat it would be to seal up all those nasty gaps. The consequence was that the Truma now had NO recirc air and literally gave up the ghost. I have now built a vent in and it works fine again.

6. The recirc air is not ducted. This means that the recirc air is taken from around the boiler having been sucked back from the habitation area. The consequence is that the whole garage would , I would have thought, tend to get warm simply because of the heat of the recirc air. Furthermore , once the desired temperature is reached the garage will be virtually as warm as the habitation area simply because of the temperature of the recirc air.

It would be nice to hear from someone else whose Truma is in the garage to confirm if this is the normal situation. 

I would imagine that a large garage area would tend to encourage the habitation area to heat up slower than a design where it is built into a smaller sealed locker. If the van temperature sensor requires more heat and that air to be heated comes from a large cavernous area like your garage then I would imagine it would tend to be colder so the heated air reentering the van would not be as warm as a system where the Truma is located in a smaller cavern where the air around the boiler is of a smaller volume.

If the garage is getting too warm then I guess ( here I go again) that it is possible that the recirc air gap is much more than 150sq cm and one wonders whether blocking off some of that gap might reduce the recirc air. It might take even longer to heat I suppose because the garage cavern remains colder.

I am guessing too much here so I will stop for a real expert to pop his head up.

Roy


----------



## JeanLuc (Jan 13, 2007)

pippin said:


> Will try the balancing act but in fact the garage one is very firmly closed.
> 
> I suppose that I ought to remove as much of the woodwork from around the boiler and visually check that all the output tubes are firmly connected.
> There are several output points in different directions.
> ...


Hi Pippin,
I don't have exactly the same situation as you because our Truma is under the wardrobe. However, from your description of symptoms, I suspect that one of the outlet pipes has fallen out of its collar where it is attached to the boiler. I had this situation a few months back and the wardrobe got really hot. This of course, is obvious since the boiler is simply pumping hot air into its immediate surroundings, in your case the garage and under the rear bed. This will also have the effect of reducing the heating to the habitation area since hot air is no longer being ducted there. The pipes / ducts are a push-fit onto collars on the boiler.

One other thought. On Hymer Camp models there was a blocking device in the duct to the alcove (over-cab). Not sure it this is relevant for you. I believe the control is behind / under the driver's seat (poss LHD) and comprised a string poking out through a hole in a plastic cap. If the string is pulled out and fastened off, it prevents hot air from going to the alcove. Once the string is released, the flap springs back to the open position. I have no direct experience of this since it does not apply to my van but that is what my general instruction book says.

Philip


----------



## pippin (Nov 15, 2007)

Thanks everybody - all suggestions/ideas taken on board.

Will be a few days before I can tackle the investigations but will relay my findings as and when.


----------



## pippin (Nov 15, 2007)

Well, problem diagnosed and half-sorted.

Dismantled all the woodwork surrounding the boiler and had a good look.

There are four take-off outlets for the hot air system.

Basically the tubes that should be a tight push-fit into them had worked loose!

There was more hot air going into the garage than into the rest of the van!

There was also a stupid bit of crushing of one of the pipes due to a piece of wood trim not having a notch cut in it.

Of course now that the weather, thankfully, has turned mild we may not need to run the heating! Will give it a blast anyway to check if the tubes simple blow off again.

We are off for a couple of nights away this afternoon so I will not refit the (cosmetic) woodwork in the garage just yet.

Will keep you posted on the results later in the week.


----------



## carol (May 9, 2005)

Pippin I hope that is it sorted - I suppose if they work lose again you could put something like plumbers mate or duck tape around and then push them on - no doubt if I am wrong - one of the guys will jump in quick.....

Carol


----------



## pippin (Nov 15, 2007)

Yes, I will try to make a more permanent job of them.

Trouble is that two of the outlets are practically impossible to get at.

The Truma site has a downloadable cut-away drawing of the boiler which is very useful.

I would recommend that anyone who has this type of boiler checks that the corrugated hoses are a really tight fit into the boiler outputs and that they have not worked loose.


----------



## carol (May 9, 2005)

I agree - but ours is set back in the corner of the L-shaped kitchen, and not exactly what one might call easy to get at - one needs to be a contortionist....

Carol


----------



## Pudsey_Bear (Sep 25, 2008)

I was thinking this weekend whilst away, could we not lose the Truma switch altogether and fit a switch to run the boiler, and another to run the heating, (a simple 2 gang) and then have a seperate thermostat, that you could site where YOU want it to be, some run on a couple of AA batteries with timer and all sorts of usual additions.

I'm not a sparky, but it doesn't seem too daft an idea, I await a boffin to correct me and make me mend my ways, but I would have thought it was more the aesthetics that would be the off putting bit.


----------



## maddie (Jan 4, 2006)

Hi Kev I am not a boffin but how are you going to get the thermostat to talk to the PCB on the boiler????
terry


----------



## Pudsey_Bear (Sep 25, 2008)

I Terry, obviously am wise in all thing Truma_* NOT*_, the idea didn't cross my mind, but as you ask, and not even having had a look into it, I would assume (rightly or wrongly) that it would be similar enough to just do it, thermostats, register the temp ,and either open or close, I have a static caravan, and when we put in C/Heating, I decided not to use the control on the boiler front, (just a timer really) I just bought a digital timer/thermostat control, took two wires (signal only, no power) to the boiler, and it worked, I think these are fairly basic pieces of kit, but know very little for sure,and I'm absolutely convinced there are one or two reading this post and are convulsing, hopefully one of them will stop laughing long enough to illuminate me/us..


----------



## pippin (Nov 15, 2007)

I think the Truma C6002 thermostat/pcb is a bit more intelligent than a simple on-off system.

If there is a big difference between actual temperature and the temperature that you select then the system works a lot harder until the temperature gets close and then it goes into quiet mode.

I do not think that you could realistically simplify the thermostat control.

Pushing the air outlet tubes back into the boiler has made a huge difference - problem solved!

Incidentally, I measured the temperature of the heated air as it leaves the boiler - it is 80C!!!!


----------

