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Truma Combi 6E electrical heating problem
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userMasterW
Posted: 13 September 2020 12:18 AM
Subject: Truma Combi 6E electrical heating problem
 
Just joined

Posts: 15

Location: 2015 Hymer MLT580 163bhp


When using my heating system on EHU, the efficiency seems to have dropped right off. I have now monitored the AC current to the HU cable, with the following results. Note that all electrical appliances except the battery charger are isolated. I am using a Fluke multimeter with true rms capability.

Excepting that the battery charger current can vary dependant on the state of charge and water heating is not selected, these measurements were taken in quick succession:-

With electrical heating off, current measured was 0.75amp.
With one element selected current measured was 2.48amp. 2.48-0.75 = 1.73 amp, at 240V this suggests only 415W.
with two elements selected current measured was 4.16amp. 4.16-0.75 = 3.41 amp, at 240V this suggests only 818W.

This is very odd because the two consumption figures are quoted as 3.9A, (900w) and 7.8A, (1800w) for the two element electrical heating circuit.
its also odd that the second heater measurement was approx double the first, even though the measurements were 50% low.

Any ideas..?

Does this suggest that one of the elements (the first switched in) is open circuit, and the 1.73 additional amps are supplying some other heater circuitry? (Plus additional battery charger current due to the fact that the fan is also switched on). The odd thing is that with only one element selected, there is still some warm air generated. So I guess it must be in circuit. So do I have a poor connection somewhere else dropping 400W, if so this would be very dodgy and a possible fire hazard.

Apart fro doubting the measurements from the meter, I suspect that something else is going on but what I know not at the moment.

has anybody else made such measurements, I would love to hear...!!!
userRobinhood
Posted: 13 September 2020 9:16 AM
Subject: RE: Truma Combi 6E electrical heating problem
 


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Location: Sherwood Forest


I'm pretty sure I've read somewhere that the elements (of which there are two) on the latest combis are both used at "half power" when the lower setting is selected (rather than using one element) in order to equalise out the usage of the elements. Patently, both elements would also then be used at full power when on the higher setting.

Should this be the case, then I would suggest one of the elements has failed.


Edited by Robinhood 2020-09-13 9:25 AM
userDerek Uzzell
Posted: 13 September 2020 9:24 AM
Subject: RE: Truma Combi 6E electrical heating problem
 


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Location: MODERATOR - 2015 Rapido 640F LHD 2.3ltr 150bhp


Truma technicians advised me that - for Combi(E) and the Trumatic C 6002EH heaters - the 230V heating elements always operate simultaneously when 900W or 1800W output is selected.

(I used to think the elements would operate independently (1 element = 900W or 2 elements = 1800W) as this seemed logical, but the Truma techs told me this was definitely not so.)
userAlanb
Posted: 13 September 2020 12:43 PM
Subject: RE: Truma Combi 6E electrical heating problem
 
Treasured contributor

Posts: 976
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Location: North Yorkshire


A simple way to operate a heating element at half power, would be to incorporate a diode in series with the element. With two elements working on alternate half cycles of the supply, harmonic contamination of the local supply system would be avoided.

Alan
userMasterW
Posted: 14 September 2020 12:22 AM
Subject: RE: Truma Combi 6E electrical heating problem
 
Just joined

Posts: 15

Location: 2015 Hymer MLT580 163bhp


Thanks for your responses. Both Robinhood and Derek seem to have hit the nail on the head, and would explain why I still get some modicum of heat from the system when 'low' is selected. Both elements would always be in circuit (unless one is open) and explains why I got the seemingly strange current readings. If both elements are operating at half power in low mode (maybe using diode or triac control) as Alan suggests, it would most certainly indicate that one of my elements is open circuit.

Anybody tried replacing the elements in one of these combi E heaters...???
userDerek Uzzell
Posted: 14 September 2020 7:12 AM
Subject: RE: Truma Combi 6E electrical heating problem
 


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Location: MODERATOR - 2015 Rapido 640F LHD 2.3ltr 150bhp


On the MotorHomeFun forum there is a 2018 ‘blow-by-blow’ account about replacing the 230V heating elements of a Truma Combi 4E - and your 6E will be much the same.

https://www.motorhomefun.co.uk/forum/threads/truma-combi-4-e-strip-down-replace-heating-elements.173899/

(It will be necessary to login to MHFun to make best use of the thread.)

There’s also this 2014 MHFun thread

https://www.motorhomefun.co.uk/forum/threads/fitting-a-new-element-in-truma-boiler.81902/
userMasterW
Posted: 14 September 2020 2:23 PM
Subject: RE: Truma Combi 6E electrical heating problem
 
Just joined

Posts: 15

Location: 2015 Hymer MLT580 163bhp


Thanks Derek, I found that link yesterday, anybody got a week to spare...??

At £300+ for the elements, I wonder what the labour charge would be... looks like an off-season job, when I am feeling in a good mood and the wife has gone to her sisters for a week.

Sounds like a pigs breakfast; looking at other comments on the web, for something that seems prone to failure, you would have thought that replacing the elements would be simple. Hey-ho, another case of very poor design.

Don't get me started, particularly on AGM battery charging, alloy wheel corrosion, rear camera quality, failure of orthogonal 3-way plastic heater pipe connections, would I buy another Hymer...H'mmm.
userBasil
Posted: 16 September 2020 9:50 PM
Subject: RE: Truma Combi 6E electrical heating problem
 
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Unfortunately the dreaded 'Truma' or should that be Trauma combis are fairly well universal now after Truma effectively bought out and discontinued the much more effective Carver system, so it's not just your Hymer thats affected.

I consider the Truma to be the biggest load of **** and the only thing on our current van that I really detest, poor quality, inefficient and regularly faulty with self destructing and overpriced electric heaters being the worst bit!!

Just my opinion of course but from experiences.

bas

Edited by Basil 2020-09-16 9:51 PM
userMasterW
Posted: 16 September 2020 10:13 PM
Subject: RE: Truma Combi 6E electrical heating problem
 
Just joined

Posts: 15

Location: 2015 Hymer MLT580 163bhp


Hi Basil, from your comments, do I assume correctly that you have been thro the replacement process, did you use a dealer, if so would you be happy (sic) to give me an idea of cost. I am not sure I want to delve into this bundle of tricks; at least with a dealer I might be able to extract some sort of warranty on the work carried out. it seems to be difficult to get any meaningful response under prevailing COVID conditions.
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