Truma heating - gas AND electric

you're right dave, it's difficult to get equipment suppliers interested when converters ignore all their fitting instructions...
it's certainly not just AS, and nut confined to Combi heater units either...however, you couldn't put our heater in a more iffy spot....
under a tall fridge/freezer (a heat source in itself) and it rests on the lower of the two floors which means it 'sits' in the heated void that is where all the heating pipes run, so it's heating itself aswell.
problems in two years, nil.
I'm sure poor installation can lead to problems but AFAIK 'overheating' is protected by a trip in the unite, an error code is generated and there is a process for recovery.
this has nothing to do with blown mains fuses...

Enter 'truma combi fuse' into Google and you'll get a host of links to problems on motorhomefacts, motorhomefun, and outandaboutlive  forums, so it's certainly not just Auto-sleeper. But of course in the total numbers sold worldwide the number that have problems is probably only a minute percentage which will never get Truma to admit a problem.

...ours certainly isn't, Sally...it just works.

Paul, the 'problems' returned by that search seem to cite power surges, poor habitation service, a failed PCB (very common) and an issue with Nordelectronica control panel (disconnect and connect and all ok)...

I'm not suggesting for one minute that these issues aren't real or that fuses don't blow, my point is that it's not heat that blows them but an excess current...

it may well be that something (unknown) is causing a surge or similar which is blowing fuses. many appliances are fused and operate at high temperatures, heaters being a case in point.

has an engineer resolving any of these issues actually said the fuse has blown (melted?) due to its hot location?

Im sure our van conversion  at 2014 is fitted with a Whale heater under the step into the cab area. Never had a problem with it but will be the first to confess to using a good old cheap fan heater to heat the van when on electric and we are present. 
         Reasoning being if it goes phut it costs £10- £ 15 to replace. With Truma combis running into  a couple of thousand+ , they are grossly overpriced for what they do imho !! Awaiting the online  beating but I'll bet  if honest we are not the only ones to do this! 

We do exactly the same with a cheap efficient 1 to 2kw fan heater, and kaspian we agree with everything you say. Overpriced and sometimes temperamental Truma Combi heater without a doubt!

Pete

Gromit wrote:But for those who have an Autosleeper with the unit shoe horned into a tiny enclosure . . . BEWARE!!

If you run it too hot using electric (with or without gas as well) there's a good chance the mains fuse will blow, and it's a real swine to get at for replacement.

No-one can say for certain, but the consensus of opinion among engineers far better qualified than me, is that the fuse is rated to run in an ambient temperature far lower than 60 degrees, and this is why so many have blown.

I would suggest using gas only if you want a fast warm up, then let it cool a little before switching to electric if on hook up.

This may be of interest.
[You must be registered and logged in to see this link.] build-up-from-truma-boiler

It’s not just Autosleeper who manage to squeeze the Truma heater into such a small space. My ageing Hymer beggars believe as to the area the Truma Combi sits in. I recently had to remove the complete unit to replace the combustion fan motor and housing and the burner, igniters and flame sensor which took just over an hour. To remove the whole unit from the Hymer to be able to work on it took 3 hours or more

Thanks Biffo

Until more verifiable evidence comes to light, I'm thinking that ventilation, or lack thereof, is key to the problem.

Even when shoe horned in, if the space is well ventilated the unit would probably function perfectly. On our Nuevo however, the only vent was half way down the front panel, and since hot air rises, the top half of the volume was a trap for all the heat build up.

Since installing the fan driven vents as high as possible I've had no further trouble . . . which I'm hoping is not coincidental! 

I spoke to Truma on their stand at an NEC show some years ago and one of their biggest grips with Hymer was the lack of space around the Truma instillation which makes ventilation a critical point during operation. I have modified the cabinets around my boiler to assist the ventilation problems and know longer get that burning smell some people have mentioned in other posts. More on Hymer forums than the A/S forum. A big advantage is my plate rack now has pre heated plates for dinner and I no longer have to put on a cold shirt from the wardrobe the other side of the boiler. 

Thanks again Biffo.

It all adds to the fund of knowledge - and it all points in the same direction as you say, " . . . lack of space around the Truma installation which makes ventilation a critical point during operation."

Dave, yes ventilation is critical, my own van isn't well placed but does have two largish ventilation grills...
however, should a unit overheat, there is a built in failsafe trip which can be reset (if necessary) or the unit allowed to cool in exceptional circumstances.
..but I've not come across any connection between 'overheating' and the 240v fuse blowing...excess current blows fuses doesn't it?
are the vans (including other brands) that have suffered blown fuses all been using mixed mode? do all of them have Sargent electrics?
to me, regular blown fuses points more towards some electric issue, spiking, etc....
even Biffo's post didn't specifically mention a blown 240v fuse or running on mixed mode, merely that Hymer (others) do squeeze their Combis into tight spaces and that might cause overheating and a trip out....
I'm certainly not convinced of any connection between mixed mode and 240v fuses blowing and googling (as suggested by Paul) is inconclusive....in fact I didn't find any link at all...

If Dare-Devil-Dennis is correct (and he's an engineer so I expect he is) those fuses are rated to run in an ambient temperature of about 25 degrees C.

The temperature surrounding the Truma unit must reach 60 degrees at least, and probably considerably higher when at full blast, so that would suggest the fuse is under considerably more strain than it should be.

I'm thick when it comes to electronics, but I know there's a relationship between temperature and resistance, and at least two other motorhome technicians have suggested that excess temperature is a contributory cause.

If the fuse is running close to its limit due to these factors, and it suffers a slight power surge, that would be enough to give it the death blow when it might have survived under less stressful conditions.

Everything about the saga is inconclusive, but it wasn't much of a job to fit the fans to the additional vents. If I get no more blown fuses it's still inconclusive - but I'm living in hope!

If you consult the derating tables for these fuses they should be OK past 100 degreesC for a current of 8 A but a small surge could push it over when hot
We had an element burn out two years ago and it was replaced by Truma at their UK HQ.  They seemed to think that there was nothing wrong with the Autosleepers installation.  If you look at the installation instructions it is fine.  If only the fuse were more accessible it would be reasonable.
We had a fuse go last year and it was a major problem to replace except by auto sleepers who seem to be well practiced!  We also had a surge protector fitted and hope that that cures the problem.
I think that it also might help to turn the right hand control to 0 and wait before changing the left had (power source) control.

Bolero Boy

I'm afraid you are quite correct in assuming you are not very welcome if you blatantly misquote and misconstrue on another forum the comments made on here.

" . . . but I'm not very welcome on that forum and don't want to move this discussion into their territory.... 
one user has put a couple of computer fans in the heater box and claims that this measure, along with never using mixed mode (it makes the heater 'too hot') has cured the fuse blowing , which happened twice I think.... "

I have been very careful never to claim that I've found a cure. The final sentence in my post above this re-affirms that standpoint. I assume you noticed that I used the term "inconclusive" twice in that one sentence alone!

If you are going to quote comments made on this forum by me or any other member, please have the courtesy to do so honestly and accurately, without deliberate misquotation and misconstruction.

Since the only possible way in which you could have made yourself unwelcome on this forum is from the comments you make and the way in which you make them, maybe you have the answer before you!

Dave, im sorry you feel that I misquoted you....you did fit a couple of fans, the problem has disappeared (perhaps you didn't specifically link the two) and you dont use mixed mode as it gets 'too hot'.....

if the fuse melting is in anyway heat related, perhaps the temperatures inside the unit when running on gas only might also be an issue.....I realise the fuse isn't 'in action' when running on gas.

this problem interested me, I also have a tight enclosure for my Combi and wouldn't want to be replacing fuses, so would like to understand any cause....

there are a couple of posters on MMM who I have great respect for, especially in the area of Combis....hence my question.
as you know, from reading the post, they wanted more info and a link to this thread....I declined as respected the privacy of those posting here..I gave my reasons and so my enquiry was kindly 'refused'.....end of story....

I can see why we (and your mates) don't hit it off, but let's not let that get in the way of a good discussion...

its so nice to see that this continues to be the most friendly forum I've ever visited....

since I joined I've had three (it might be more) private messages from the 'mods" basically telling me to * Inappropriate Word * off......yes, definitely the most friendly....

I'm never rude, don't abuse any posters, try to post to the best of my knowledge and give an alternative view to problems where (in the main) posters only have a single view of the issue....the AS view.

however, this doesn't sit well with yourself, Roli and Peter who run this forum.

I've had offne converastions with several posters on this foum and have found them to be pleasant and intersting folk, shame I won't be debating issues with them 'in the open'

I wish you all (except the three who've been so (not) pleasant and welcoming to me under cover of private messages) well with your vans and your travels...