Truma heating - gas AND electric

Hi everyone

Newbie question here but could someone explain how the heating works when the power source is set to both gas AND electric.  Does it boost on gas then automatically turn to electric (when on hook up obviously).  Does it then switch backwards and forwards, or just stay on one?

It may seem really obvious but I’ve read the instructions and can’t quite grasp them. 

Many thanks.

I’m no expert but ours you control on hookup a switch /gage by door, if you use gas you just use controls on fire on gas it does use some.

It goes like a jet engine Sally, running on gas and electricity at the same time.

Always sounds a bit iffy to me, but it's designed to run like that for a very quick heat up when the van is very cold. And quick it is . . . you could do toast at the air outlet!!

It doesn't automatically change to electric you have to change it yourself to either gas or electric. Use the dual fuel setting to warm up quickly and then switch to either source to maintain (gas is always hotter but if on hook up included in pitch price then it's ibvobvi which to choose).

It doesn't automatically change to electric you have to change it yourself to either gas or electric. Use the dual fuel setting to warm up quickly and then switch to either source to maintain (gas is always hotter but if on hook up included in pitch price then it's obvious which to choose).

burlingtonboaby wrote:

Paulmold wrote:It doesn't automatically change to electric you have to change it yourself to either gas or electric. Use the dual fuel setting to warm up quickly and then switch to either source to maintain (gas is always hotter but if on hook up included in pitch price then it's ibvobvi which to choose).

Ibvobvi Paul.  
Boaby

Autocorrect/autocomplete drives me mad , failed to read through before sending, corrected now.

Ah HA!  I hadn’t realised it ran both together at the same time. 

I thought it was hot (I tried it).  So that makes sense, when it’s really cold a BOOST using dual fuel, then switch to preferred fuel (which on hook up is electric you’ve already paid for).

Got it!  Thanks 

on a combi 4kw set to mixed mode 2, the unit will supply 2kw of gas power and 1800w of electric.
it will use both sources to realise the temperature to the required level and then the gas burner will AUTOMATICALLY ease back, leaving only the 1800w electric to maintain the temperature.
if this is not possible (too cold outside) then the gas burner will fire back up AUTOMATICALLY adding as much gas as required, up to its max of 2 kw.
setting the unit to Mixed 1 only includes 900w of electric power, good for low power sites.
a Combi 6 unit works the same but can supply upto 4 kw of gas.

EDIT.....from the Combi operating instructions


In mixed mode 230 V electric mode is preferred if the power requirement is only low (e.g. for maintaining the room temperature). The gas burner is not enabled until the power requirement is higher, and is the first to switch off during heat-up operations. 

I've just been to my van (same van as Sally, similar age) to check my Truma instructions and the final sentence is not there. Perhaps the instructions have been updated or the operation amended on later systems with digital control panel for the combi. Our vans have the old style dials and no digital display. 
It hardly matters anyway as it chucks out so much heat in our comparitively small vans that we are more than likely going to turn off dual fuel heating before the thermostat does it for us if thermostat is set at highest level as is likely when you're trying to heat up a cold van.
There are also several instances of 'lost in translation' in the Truma manuals.

while I agree it probably doesn't matter in such small vans, it may be of use to those with larger ones.

AFAIK, mixed mode has always worked as described and we have had four Combis dating back to 2007 complete with rotary dials.

I checked my instructions for my Truma Combi 6E on 2017 Warwick Duo and the description supports the statement made by bolero boy (page 5). i.e. in mix2, gas is not enabled until the power requirement is more than that which can be supplied by electric only (1,800W), and once power requirement drops then gas will be switched off.

Also I think its interesting to note that the specs (page 8) show the max outputs are
  Mixed 2    5,800W  (4,000+1,800)
  Gas only   6,000W
so the max output is gas only mode. Slightly counter-intuitive I think.

So I think if I'm in my van freezing my bits off, then I will use gas only mode for max heating until heated up, then manually switch to elec 2 if EHU is included.

From our experience, Don's point is quite reassuring.

Having had the notorious mains fuse blow twice already, possibly (probably?) due to being run above it's design limit, I would not use gas and electric together.

I hadn't perused the instructions, but gas alone is more than adequate to warm our van up very quickly (without risking the fuse). I hadn't realised that (in theory at least) it provides more heat on gas alone than when running both energy sources together.

but Dave, in mixed mode the unit is running below its max capability as I (and Don) have posted.

for a combi 4E....the max is 4000w on gas only.
the same unit can provide 2000w of gas and 1800w of electric when on mixed mode...total 3800kw

for a combi 6E. the gas only output is 6000w
in mixed II mode its 5800w as in Dons post (4000w gas plus 1800w electric.)
it's also designed to regulate the appropriate power input depending on temperature and requirement....AUTOMATICALLY.

Dave mentions a jet engine which gives me some comfort.
On holiday in Austria recently our ACSI card only covered 4kwh per day so we used gas only for heating. On one isolated occasion I turned the thermostat up to maximum (we have the 2 dials controller) and after a minute or two the heater sounded like a banshee - the fan was running really fast and very hot air was coming from the vents. It was so unusual that I was very concerned and switched off immediately. After half an hour I switched on again and this time there was no violent reaction and the heater has not gone ape since.

Yes Ron.

All the quoted figures and admonishments about capacities and whatnot go nowhere toward describing the actual experience.

When it's running at full chat (that's maximum capacity for those who prefer!) it sounds very alarming, and the blown air is too hot to hold your hand in for long. 

the Truma is a very interesting beast and takes some understanding.
the normal operation of heating with older (pre CP plus) versions is for the fan speed to be proportional to the amount of heat produced and the temperature level set.
on low heats (900/1800 electric) the fan generally runs at lower, fairly gentle speeds.
on mixed or gas only modes, there is far more heat to dissipate and the fan will run at higher speeds.
all fan speeds are controlled by the unit.
with the new CP plus system, the user can select the fan speed, combining lower heat levels with higher fan speeds, this gives a 'better' output when on low level power.
however, when the heater has (for example) been used to heat water (the unit is hot) and heating is then selected, the unit needs to evacuate the heat from itself and this is when the 'jet engine' sound is heard....
the unit is removing the excess heat from itself and this is done via the heating pipes...
after a short time, 30 seconds to a minute, the fan starts to slow down and settle at the appropriate rate for the selected heating function.
by turning the unit off when the fan spins fast, the user is preventing the unit from cooling itself...just leave it and it will gently return to the correct speed...
this high speed fan activity is a perfectly normal part of Combi operation, nothing to be alarmed about.

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.]

my own Truma unit isn't (doesn't seem to be) sited in the best possible location, under the fridge/freezer, so ventilation no better then many other converters.
there are two ventilation grills which may provide what Grommit has done but there are no fans.
however, the unit hasn't missed a beat in the nr two years we've had the van.
I don't see how you can (or can't) run the unit 'too hot'....if you need heat, the unit WILL get hot, very quickly...
In winter, ive left it running (on low) while we've been out all day and there's never been an issue.
I can't see that a Combi fitted to any AS van should be any different.
if they are, then customers would want to know, wouldn't they?
why would a 'mains fuse' in an AS blow when it won't in other installations...?
I've had Combis in two Swifts and two Carthagos and have never had a mains fuse blow...have I been lucky, or is there something else afoot in (perhaps) the way the AS/Sargent system links to the Combi?
if anyone is having issues with their Combi then it needs to be resolved by the dealer, like any other problem..
avoiding using it or not using it to its full potential can't be the way to go forward, can it?

Gromit wrote:Yes Ron.

All the quoted figures and admonishments about capacities and whatnot go nowhere toward describing the actual experience.

When it's running at full chat (that's maximum capacity for those who prefer!) it sounds very alarming, and the blown air is too hot to hold your hand in for long. 

hanks, Dave
That reassures me that nothing was wrong but if it happens again I will still switch the b@!![You must be registered and logged in to see this link.] off and let it cool down.  I don't want the mains fuse to be melted by a hot blast of air, nor do i want it to trip given the position of the reset switch.

Bolero boy wrote:why would a 'mains fuse' in an AS blow when it won't in other installations...?
I've had Combis in two Swifts and two Carthagos and have never had a mains fuse blow...have I been lucky, or is there something else afoot in (perhaps) the way the AS/Sargent system links to the Combi?
if anyone is having issues with their Combi then it needs to be resolved by the dealer, like any other problem..
avoiding using it or not using it to its full potential can't be the way to go forward, can it?

My sister had the mains fuse blow in her Swift and my neighbour had the fuse blow in his Dethleffs. Both out of warranty and so difficult to get at that they both used gas only afterwards. I'm sure you visit other forums and you will therefore find threads on the same subject, I've seen many over the years.

bolero boy wrote:I don't see how you can (or can't) run the unit 'too hot'....if you need heat, the unit WILL get hot, very quickly...

if anyone is having issues with their Combi then it needs to be resolved by the dealer, like any other problem..
avoiding using it or not using it to its full potential can't be the way to go forward, can it?

So what's your theory on why so many fuses have blown , and how can the dealer be reasonably expected to resolve a problem that's way beyond his control?

I don't know Dave...
my own brands forum doesn't report occurrences of this happening and the fuse is the same I would imagine.
perhaps the fuse should have a higher 'heat rating' if this is the apparent reason for failure...
for sure, temperatures inside and adjacent to a MH heating unit will be far higher than 25 deg...as posted above, at full chat you can't put your hand nr an outlet...   
I'm sure my own install isnt particularly efficient at losing heat in the unit housing but I've never had a fuse blow, nor heard of one failing, you make it sound like it's an everyday thing on here...it shouldn't be.....should it?
whatever the issue, I'd be getting my dealer (and Truma if they're not able to make a diagnosis) all over it if it failed in this way. 
we are customers and this level of service (pr lack of it if ypur heater isn't functioning) isn't good enough...
we don't need to keep making excuses for suppliers and dealers.
MHs cost plenty and we pay for working ones, don't we?

If a fuse blows and the replacement fuse works fine then I would look at the fuse as the problem rather than the heater itself.

My manual specifies the use of a 10A slow blow fuse but apparently some versions of the manual specify a fast blow fuse.  I guess using a fast blow fuse may mean the fuse blows when there isn't an actual fault.

Hi Don
I've always wanted to use the word "obfuscate", and this is a good opportunity! 

Nothing about this seems obvious or straightforward, but it is a cast iron certainty that no individual owner (or even dealer) will have any effect in getting Messrs Truma either to admit to a problem, or do something about it.

The tiny, poorly ventilated enclosure seems to be the most likely cause, but Truma would have to "sign off" all manufacturers' installations at the prototype stage or before, so the fundamental blame has to lie with them. Assuming there's nothing wrong with the units themselves, that can only leave the installation as the most probable cause.

All I can add to the saga is that after three weeks in a rather cold Scotland, and using my fans whenever the Truma was on using the mains, the fuse hasn't blown again . . . . yet!!

"Tenterhooks" is another good word, and whatever they are, I'm on them every time I turn on the space or water heater!!