Truma Combi 6E electrical heating problem

[colin]

I've never used a van with a Combi which doesn't have the 'pungent electric' smell, this has always been when on hot water heating only with the space heating fan stopped, so in some respects the dealer is correct, BUT, I would say it's because I've also never seen a van where Truma's installation instructions are fully complied with.

I first came across it on a WildAx, and was so concerned that we stopped using the heater until contacting the hire company. On our van, if heating water only, I close the two highest(and they are also shortest) butterfly valves.

[Derek Uzzell]

MasterW - 2020-10-05 10:47 PM

 

...Unless I am mistaken, when the elements are switched off by the control system, the circulating fan also cuts, leaving the element surroundings to overheat for a period of time because the cooling effect of the circulating air is no longer available...

 

 

When a Truma Trumatic-C or Combi appliance is in water-only heating mode, there is no forced airflow over the appliance’s heat exchanger, and this is the case irrespective of whether water heating is via gas or 230V. The only time air is driven over the heat exchanger is when blown-air heating has been selected and the appliance's air-circulation fan is running.

 

These appliances have two fans. One fan circulates air within the leisure vehicle and the other - sealed from the leisure vehicle’s interior - sucks air into the gas burner and blows it out though the burner’s exhaust. (I’m sure you are aware of this, but there’s been confusion about it here in the past.) The heater’s air-circulation fan may run for a while after the heater has been shut down, but that's the only ’cooling’ that’s normally done.

 

Good luck with your discussions with Truma.

 

(I’ve added the missing drawing to my previous posting.)

[MasterW]

Hi Derek,

 

Have viewed the drawing, will lift the seating and inspect. Yes, I am aware of the two different fans. I am specifically discussing the hot air circulation, not the forced air for the gas burner. Your comments and those of Colin, reinforce my suggestion that it is during the periods when no warm air is being circulated, the smelly air is being generated. What makes it difficult to locate is that the smelly period is not so noticeable until the warm air circulation switches on. In all my experience I can not conceive that the pungent smell is 'OK'. Some long term (maybe not so long) damage is taking place and most certainly should not be in evidence at all. Once I lift the seating, I will check the resistance of the elements if possible.

 

I had the warm air only, set at 2 elements, 16 degrees all last night and there is no smell whatsoever. I have now switched of the warm air and put the water on 60 degrees. will check for smells later. There is of course now only one element in operation even though I have called up two. Maybe the smell was coming from the now defunct element.

 

PS. your diagram note on short duct lengths suggests the sump is to stop unwanted hot air from circulating, not unwanted smells.!!

 

[Derek Uzzell]

As I said earlier, ‘smelliness’ has been a common complaint with Truma Combi heaters, with some being worse than others.

 

https://tinyurl.com/y6bxfjmv

 

This November 2019 C&MC forum entry discussing an extreme case with a Combi in a new Swift caravan when operating on 230V.

 

https://www.caravanclub.co.uk/club-together/discussions/information-technical-tips-advice/caravans/truma-combi-hot-plastic-smell-venting-into-caravan/

 

You’ll note that the advice from a Truma technician included having a ‘kink’ in the air ducting, though that should only be necessary for ducts less than 50cm in length.

 

This 2017 thread covered the same ground

 

https://www.caravantalk.co.uk/community/topic/123347-truma-combi-6e-burning-smell/

[colin]

I should note that whilst the smell would indicate that it is electric related, it isn't, whilst other vans we used have sometimes had electric elements, our present van is gas only, and the other vans have produced the smell whilst on gas only as well as on electric. I think it is a plastic part, probably on outlet, getting very hot.

[MasterW]

Colin, with respect, I think you may be wrong. The smell to me is not a hot plastic smell but an ozone type smell similar to that when a motor brushes are arcing or even the smell of a striking match.

 

For your information. I have carried out further tests. With the water heating switched off and with the only energy source 240V, 1 element; 18 degrees, mediocre warm air heating was available, hardly detectable. With 2 elements, slightly warmer air was available. This 2 element situation was left in place overnight with no sign of the pungent smell.

 

During the following morning, I switched off the warm air and selected water heating only, 60 degrees, 2 elements.

 

After a period of time (1-2 hours), 60 degrees was reached but there was a strong pungent smell in the motorhome, particularly in the bathroom. I therefore concluded that the smell was indeed generated by the electrical heating and only with the warm air heating switched off, i.e. When no cooling air passes through the heater.

 

You will say that this test is not conclusive.

 

I will of course now try the same type of test with the energy source being only gas. I will report further results.

 

[MasterW]

Right chaps, here comes the humble pie bit...

 

I ran the warm air heater all last night on eco, gas only, set to 16 degrees, with water heating off. There was no discernible smell anywhere in the motorhome. So I switched off the warm air heating and selected water heating only, 60 degrees, gas only.

 

Within 30 minutes the water was up to temp and the van stunk..!!!

 

So my conclusion is that whatever energy source is selected, it is the heating of water that creates the smell. In my defence, when warm air heating and water heating are selected together, the passage of air blown through the heater seems to minimise (if not entirely stop) the smell but most certainly when heating water only, whether gas or electricity is used, the pungent smell is created.

 

I can only assume that there must be a sensitive area somewhere in the heater which is subject to very localised overheating problems. When air is blown through, it limits or indeed removes that localised overheating hotspot.

 

This does nothing to excuse the problem, it is diabolical to expect the motorhome owner to accept this situation. My case may well be worse than some others but none should accept this situation.

 

Many folk have had to replace electrical heating elements in a relatively short period and many folk have had to put up with the pungent smell. Whether these two issues are linked in some way or not, neither problem should be built into these heaters.

 

To be continued.....

[colin]

As part of my 'day job' I have to come up with solutions to engineering problems, if I put my mind to it I might well be able to come up with a solution, but as I've found after a decade of using Combi heaters this doesn't appear to be a dangerous problem, and as the answer is as simple as closing a couple of butterfly valves, I cannot find the enthusiasm to expend any energy on it, and to be honest we don't use the water only heating option very often. In fact I looked at changing the short, rising, air outlets but couldn't be bothered, maybe I'm just lazy.

Someone did once post that the problem was the heat getting to the plastics on the air outlet, if this is the case then making the first part out of metal, then extending the individual pipes before they change to the flexibles would seem to be a fix, but Truma must be aware of the problem and must have looked at this.

[MasterW]

Hi Colin,

 

Trouble with closing a butterfly valve, it also closes any heat input to our washroom, which thanks to Hymer, is separated from the remaining habitation with a very nice, close fitting door.

 

Travelling abroad in spring/autumn (ACSI sites) and UK in the summer, also means that I do not very often, deliberately have just the water heating on. However, it is not that simple. When both warm air and water are selected together, the control system selects where the energy is directed, depending on the demands of the two systems. it is entirely possible, that with habitation up to temperature, water heating only will take place and hence generate the pungent smell, which is then circulated when the warm air switches on again.

 

It is this on and off condition that seems to generate the confusion as to which part of the system and which energy source generates the smell, although it is now clear to me.

 

As matter of interest, two of the warm air outlets (on the same side) are enclosed in insulating jackets while the opposite side outlets are just flexible tubes. The two non-insulated outlets disappear in short thrift under the floor. The smellier washroom outlet is one of the insulated tubes. see attachment. Sorry don't do attachments <100kb

 

Regardless of where the smell comes from, I have I think, one of my elements open circuit and therefore to carry out any replacement, the heater will need to come out.

 

Best of luck with your day job, sounds very similar to mine, only I have now retired..!!

 

I will continue this post in the coming weeks once I have gathered more information.

[Derek Uzzell]

Fourteen years ago thare was a major safety recall relating to Trumatic-C combination air/water heaters. This was mentioned here

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Truma-Safety-Recall/4470/

 

and I commented at the time

 

...I'm pretty sure this is a further attempt to fix the smell-while-heating-water-on-gas that has been complained about with Combis since the Year Dot. My previous 2001 C3402 did it and, despite being told that a change of material had solved the problem (basically caused by heat-soak), my 2005 C6002EH does it too. The smell of 'cooking' plastic has lessened somewhat with use, but it's still present.

 

It was/is an unpleasant ‘characteristic’ of Trumatic-C appliances and also of the Combi successors. Truma are well aware of it but seem unable to suppress the smell completely.

[MasterW]

Gone back to basics:- Forget the smell for a moment.

 

The following figures are current draw on the EHU this morning with cold water in tank.

 

1) Warm air & water off. 0.23amp

2) Water1, 60 degree selected. 0.23amp

3) Water2, 60 degree selected. 3.79amp

4) Water1, 40 degree selected. 0.23amp

5). Water2, 40 degree selected. 3.79amp

 

Conclusions.

 

a) With water1 selected, no additional current is drawn.

b) With water2 selected, an additional 3.56amp is drawn.This equates to approx 850W. This should be 1800W.

c) There is no additional current drawn when changing from 40-60 degrees.

 

This suggests that indeed, one element is open but it makes it difficult to understand how the two elements are controlled. If both are in parallel and/or controlled using 1/2 power circuitry, with one element open I would have expected to see 1.8 amp (850/2/240).

 

The plot thickens:-

 

1) Warm air and water off. 0.23amp

2) Warm air1, 20 degrees, eco, selected. 2.12amp

3) Warm air2, 20 degrees, eco, selected. 3.74amp.

4) Warm air1, 20 degrees, high, selected 2.12amp

 

Conclusions.

 

a) From the water1 only test, assuming that no current flows through one of the elements, 1.89 amp is consumed by some other circuitry when warm air1 is selected, maybe the fan drive.

b) When warm air2 is selected, an additional 1.62amp is drawn, which equates to 388W.

 

With water only selected, only the small fan at the top of the heater is operating.

With warm air only selected, both the small fan and the air circulating fan operates.

 

The operational effect of these two fans is specific and with water only selected, the top of the heater, around the gas exhaust outlet gets too hot to touch.

 

With warm air selected only, the cooling effect of the air circulating fan is very noticeable. After several hours there are no areas of the heater that are too hot to touch.

 

Note that during all of these 240V only energy source tests, there was no smell evident, accepting that only one element is operational.

 

Anybody got any more thoughts...!!!

 

[Derek Uzzell]

This link describes how a Combi-E heater functions

 

https://www.zwiebelfam.nl/en/truma-combi/

 

and shows the positions of the combustion-air fan (5) and the warm-air circulating fan (10).

 

What I had not appreciated was that above the combustion-air fan is another fan (that presumably is there to cool the PCB) as shown in photos attached below, but I’m not sure if that fan is there on all Combis or on just the “E” versions.

 

At one of the NEC shows I asked a German Truma rep if he could explain how a Combi was ’throttled’, as my Combi 4 seems to have a mind of its own and adjusted its blown-air fan speed quite differently to my previous Trumatic C6002EH heater. A cut-open Combi was on the Truma stand and the rep showed me where the internal sensors were and said (essentially) that you just had to let the heater do its own thing.

 

I also asked one of the Truma(UK) reps that I’d known for some time “Do you really know how a Combi works?” and he said “No - I used to know how the Trumatic C heaters functioned, but the Combis are much more electronicy. It’s like trying to understand the technicalites of a smartphone."

[MasterW]

Derek, not sure which are your fans 5 and 10 but in my Combi 6E which looks identical to your main pic.,

 

From my 240V (only) energy source tests yesterday:-

 

The small white-bladed fan is a component cooling fan and runs when I select electric water heating1 or 2. The much larger caged fan down to the right in your pic is the warm air circulating fan and comes on in conjunction with the white bladed fan when I select electric warm air heating1or 2.

 

The third fan, behind the white bladed fan, I think is the gas burner fan and I believe only spins when gas energy source is selected. I think it draws in air for combustion and forces the spent gases out thro the input/output vent on the outside of the van.

 

As I mentioned yesterday, the area around the gas exhaust pipe (the alloy tube above the large caged fan), and in particular the jubilee clip holding on the input/output flexy, gets too hot to touch after an hour or so on water only, heating2. It can only be conduction heating because the gas burner fan does not run on 240V, so little or no air is blown thro when electric water heating only is selected.