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Truma Combi heaters


Guest Derek Uzzell

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Guest Derek Uzzell
This refers back to postings by John Steggles ("Truma combi heater" 13/02) and Tony Smith ("FFB Classic" 08/02) John Steggles & Peter Goddard: I asked the Truma technicians at the NEC to talk me through retro-fitting a 230V/450W heating-collar to a Combi. Assuming (and it's a big "assuming") you have sufficient in-situ access to the heater, the procedure is as follows:- 1. Disconnect the blown-air fan's cables where they join the heater's wiring-loom. 2. Undo and remove the recessed nuts around the outer edge of the heater's top surface. The upper part of the heater, together with the blown-air fan-unit, can now be lifted free. 3. Detach and remove the black moulded-composite 'skin' that forms the heater's protective/cosmetic outer casing. The heater's water-tank will now be revealed and the heating-collar is fitted by simply wrapping it around the tank's outer surface, linking the collar's ends together by the spring retainer provided in the kit. The outer casing (see 3 above) has a perforated 'cut-out' section. Remove this to allow the orange 'box' carrying the collar's thermostat and 230V connection-cable to protrude through the casing. (Note: before removing the perforated section, confirm that the collar's 'box' will end up in a suitable position in relation to the heater's installation. If it doesn't (clearance difficulties perhaps?), then an alternative hole will need to be cut in the heater's outer casing.) Carry out processes 1-3 in reverse order, then connect the heating-collar to a fused/switched 230V power-supply. And that's essentially it. As Truma rightly emphasised, potential risks arise should the Combi heater need moving, as this task normally involves disconnecting the gas supply and probably the exhaust flue too. Disconnection isn't the problem: it's the failure to reconnect gas supply or flue (or both!) properly that can lead to disaster. The exhaust flue should always be fitted with a new O-ring following any disassembly and the gas-system should be leak-tested after reconnection by someone competent to do so. I moaned to the Truma guys about the £192 cost of the heating-collar retrofit kit and the consensus was that £70 would be a more realistic figure considering how simple the thing is. (Frankly, this is an exorbitantly-priced gizmo when one considers the £267 difference in price between a basic gas-only Combi C6002 and the latest all-singing-and-dancing C6002EH model, while £306 will buy you a complete, fully-insulated, 14 litre 230V-only 850W Truma "Electroboiler".) On the question of water-heating times, I subsequently looked up data for an early Truma-Ultrastore 10 litre boiler that was fitted with a 230V/450W immersion element. 70 minutes was given as the approximate heating duration to attain 70C, so I would guess bringing a Combi's 12 litres of water to 60C via a 450W collar would take about as long. Tony Smith: Regarding your Combi's air-shifting difficulties, Truma's advice began with the obvious - check for kinks, crushes or blockages in the air-trunking and confirm that the heater itself can suck in plenty of air. (You might also check for the presence of closed "throttling" butterfly-valves deliberately placed in the air-trunking to permit balancing of the air distribution. It's a long shot, but one never knows!) Truma didn't think a 14' trunk was excessively long, provided that it was reasonably straight - but lots of tight bends would reduce the air-flow rate significantly. Certainly, if several air-outlets were temporarily closed, it was anticipated that there would be an appreciable increase in flow rate from the outlets remaining open. You may well have noticed in March 2005's "Motorhome Monthly" magazine that the C6002-based heating system fitted to their road-test Auto-Trail Cheyenne 840 exhibited similar symptoms to yours (hot air at back of vehicle, cool air at front) - so you're not alone. If everything about your heater and air-distribution system proves to be OK except for the layout of the air-trunking, I suggest you install a Truma Multivent-fan TBM (Part No: 41141-01 and about £71 in the UK) in the long trunk. This unit is multipurpose, including (quoting Truma's product leaflet) "increasing the air output in particularly long warm air duct systems". That should do the job. General Comments (for anoraks only): I noticed that changes have been made to the latest Combis compared with my own 2000-model C3402 heater. In "Winter Operation" (ie. when the unit is providing blown air) the control-panel now permits heating of air + water OR air-only. Older Combis always heated air + water while in Winter Operation mode. In certain circumstances, this extra function should reduce gas usage somewhat. Historically, Combi heaters had the air-temperature sensor built into the control-panel. Because of this, Truma's common-sense advice was to install the control-panel in an unobstructed location away from direct heat and draughts, about mid-way between floor and ceiling. However, this advice seemed to have little impact on motorhome converters, many of whom just put the control-panel where it was easiest to stick it (rather like they installed the Combi heater itself.) For about £25, it was possible (and easy) to fit a remote air-temperature sensor that could be positioned optimally, but this option was seldom employed. The control-panel of current Combis no longer carries an air-temperature sensor and a remote sensor is now standard. (If you want to play Spot the Sensor, it's a small black domed-head buttony doodah.) In theory, this should make things simpler for the converter to follow Truma's advice: in practice, it probably will make little difference and the remote sensor will be positioned next to the control-panel. (Eura Mobil's Profila is a prime example of this, with control-panel and remote sensor in close proximity at ceiling height above the living-area's entrance door.) Truma's NEC stand offered the opportunity to inspect a 'sectioned' example of their recently-introduced Combi C6002EH heater. This addresses long-standing complaints (mainly from UK campers I suspect) that Combis had no mains-powered electric blown-air capability. C6002EH's design incorporates into the finning of the central heat-exchanger 2 x 230V/900W elements. These can be operated individually or in tandem to provide blown-air and/or water heating, and can be combined with gas operation if required. I've developed a definite wariness of combination air/water heaters after traumatic experiences with Atwood and Truma examples, though it hasn't stopped me choosing another Combi-equipped motorhome (Hope springs eternal and all that.) So I was seized with dreadful foreboding when I first heard of C6002EH's extra complexity. The Truma technicians told me they had been similarly apprehensive initially, wondering if it would be possible to discriminate between 230V-related faults or gas-related ones - but they were now confident this would not be a problem. As a self-confessed technophobe I prefer simplicity when I can get it, and C6002EH ain't simple. There are now 2 discrete electronics-boards - one handles gas-only processes and the other 230V + gas functions - and 2 different control-panels. Truma claimed the gas and 230V sides were essentially separate, and a fault on one side was unlikely to affect the other. I said I was far from convinced by this argument, but time will tell who is right. Frankly, if I were a Truma tech I'd be more concerned over future telephone calls from C6002EH owners who can't understand how to operate the thing than specific fault diagnosis. (This view is backed by confidential anecdotes that I better not repeat.) Returning to the Auto-Trail Cheyenne 840 test-report I mentioned earlier, this said "The boiler is also a little noisy when firing up and cutting in as the temperature falls." I reckon that this type of noise is quite common with Combis and, when it happens, I believe motorhome owners may well be told it's normal and must be tolerated. Our Herald's retro-fitted C3402 used to make all sorts of strange sounds when the gas burner fired up, whumping, whooshing, cow-in-distress mooing, etc. This antisocial behaviour persisted through removal/replacement of the heater to cure a water leak, only ceasing after the burner-assembly later failed and the repair work included replacement of the exhaust-flue's outer duct. (Perversely, after the heater went quiet we then used to worry whether the gas had actually ignited!) As a Combi fires up on gas much like a modern Dometic automatic-ignition fridge, there is really little reason why it should be any more noisy when doing so. Truma's experience indicates that the cause of 'fire-up' noise is normally due to the manner in which the heater's exhaust-flue has been installed, and it should be comparatively easy to correct the problem provided that one can access the heater to do it. A technician reminded me that Truma's warranty excluded the "Additional costs based on complicated removal and installation conditions of the appliance (eg. removal of furniture or parts of the vehicle body)". So, if you've got a noisy Combi and your 'van's manufacturer has constructed the vehicle around the heater, don't expect Truma to pick up the bill for the major surgery involved in getting the beggar out and back in. Lastly - muck! Combi's are sensitive to insects crawling into the exhaust-flue: spiders' webs in the flue can affect a heater's proper functioning and, if the insects reach the gas combustion chamber, they can clog up the gas burners. So fit a cover to the flue's outlet if the vehicle is laid up for extended periods. There have also been reports of 'oily residues' that have collected in gas-bottles finding their way into Combis and stopping them in their tracks. Apparently Calor steam-clean empty bottles before refilling them, but other bottled-gas suppliers may be less hygienic. I've seen it suggested that using a long gas-hose to form a 'swan-neck' between fixed-regulator and bottle, or between on-bottle regulator and the vehicle's fixed gas-tubing (dependent on which type of system one has), can help. The logic is that the oily muck collects at the swan-neck's lowest point and regular cleaning of the gas-hose's interior prevents the residues building up and entering the heater.
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Guest john steggles
Thanks Derek for obtaining a comprehensive procedure for retrofitting a 240V heater collar.Hopefully I shall attempt to fit one when the weather is a little kinder to DIY !!
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Thanks Derek - How could I have missed it!I've just looked at the trial on the Auto Trail in MHM and it's exactly the same problem as mine. The hot air comes too hot from the two nearest air outlets and virtually not at all from the others. I'll check for kinks (and for troggs), but I think the problem must come from the positionment of the boiler. In the installation instructions it says the boiler should be positioned centrally for best results. A 3402 model would surely have been capable of doing the same job (ie heating 2 outlets)so I don't see why a 6002 was originally fitted.
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Guest Derek Uzzell
John: 1. Good luck with adding the heating-collar. 2. I belatedly noted your question about tyre-wear. Although you should anticipate significantly higher wear on your Hobby's front tyres compared with the rears, 22,000km is still a short distance for the degree of front-tyre wear you mention (for Michelin 'camping' tyres or any other type/make). Wear on the inside edges of front tyres is usually an indication of excessive 'toe-out' (ie. like a ballerina's feet!). As the tracking of front wheels is normally set parallel or with a small amount of 'toe-in' (ie. pigeon-toed!), you should certainly get the tracking checked. The correct tracking value will relate to the Fiat element of your motorhome and it shouldn't matter that it's a Hobby or has an Al-Ko rear chassis. A Fiat commercial dealer ought to be able to provide you with the recommended tracking figure. (You might be interested to learn that Pilote make a tracking-check at 1500km an obligatory condition of their warranty.)
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Guest Derek Uzzell
Peter: If you do decide to go ahead, try Miriad Products (www.miriad-products.com) for a discounted price. This firm is actually next door to and shares warehouse space with Truma(HQ) and is the primary UK distributor for Truma products. At the NEC show I asked the Truma chaps about how much their trade discount was. The reply was "About 20% depending on what one bought, but Miriad's normal best prices tended to be much the same." With discount, if you don't ask you don't get.
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Guest Derek Uzzell
Tony: You ask why a Truma C6002 was fitted to your FFB rather than a C3402. Two reasons spring to mind - output-power and bangs-for-bucks. C3402 has 2 heat-output levels - 2kW or 3.4kW - and a maximum air flow rate of 203 cubic metres/hour, whereas C6002 has 3 levels - 2kW, 4kW or 6kW - and a flow rate of 287 cm/h (though it needs saying that these flow rates are 'free-blowing' with no air-trucks attached to the heater.) So a C6002 can move significantly more and hotter air than its baby brother, resulting in a marked reduction in the warm-up time of a leisure vehicle's living space: this is a useful benefit in a vehicle with a large interior-volume. Additionally, with a long vehicle, a C6002's more powerful fan should (ought to!) be able to push the hot air into distant corners. Price-wise, the present UK full retail price (VAT inc.) of a gas-only C3402 (without a flue-kit) is £1021, while a gas-only C6002 costs £1178. Now, if you consider the discount a motorhome converter will get when bulk-buying appliances, the price-difference between the two Truma models will be peanuts. (If I were a cynical chap, I might also suggest that offering a C3402 heater in a 'van's basic specification and a C6002 as an extra-cost 'upgrade' could provide a nice little earner.) The C3402 retro-fitted to our Herald used 3 of the 4 ducts in the heater's base, feeding 5 air-outlets (1 in bathroom, 4 in living-area). The appliance was near the 'van's middle but crammed in a below-wardrobe cupboard. During the installation (by Truma(UK)) deliberate thought was given to equalising air-trunking lengths as much as practical (which made the base of the heater-cupboard resemble an Anaconda Love-in) and I had installed large grilles in the door and upper surface of the heater-cupboard to aid warm air recirculation. The only 'butterfly' valve in the air-trunking was in the bathroom outlet (little point having a sweltering bathroom except when it's being used). Plenty of air came from all the outlets simultaneously and we had no complaints about the C3402's efficiency (reliability was another matter). However, the Herald had a quite small internal volume and we used to curtain off the complete cab area when the weather was really chilly. It seems from the MHM Auto-Trail test that even a C6002's 6kW output can be inadequate when the appliance is installed well off-centre and I'm sure you'd find a C3402 in your FFB would struggle even more than your present heater. If you want extra warmth at the front and the heater currently can't blow it there, it's going to be a lot easier (and cheaper) to fit a Multivent fan to give the C6002 a helping suck than to attempt to re-jig the complete installation. The Hobby T-600 FC camping-car I'm buying has a C3402 as standard, installed beneath the front of the rear 'French' bed and feeding 2 nearby outlets (for bathroom and bedroom), plus 2 more towards the front of the vehicle in the lounge area. (Also an engine-coolant fed heat-exchanger for en route living-area heating.) There is an optional upgrade to a C6002 that the German Hobby dealer advised as "non-essential but nice to have if you go skiing." Although we don't ski we do like being comfortable, and, even though this Hobby design is relatively compact, my experience with a C3402 was that we would probably appreciate the C6002's faster warm-up potential - so I chose the latter. Now, after our second visit to the NEC and a lengthy chat with a long-suffering Truma representative (my wife decamping to a distant bench to avoid contracting Technocoma), I've decided to opt for the new C6002EH if it can still be added to our order. (Yeah, yeah, I know I said I wouldn't have one - but New Millennium Man is forever being encouraged to recognise the feminine elements of the male psyche, so I'm just following advice and bonding with my female instant-mind-changing aspect. Anyway, I've never claimed to be rational - logical maybe, rational no.) When I discussed C6002EH previously I was right about the heater's design but wrong about the 2 control-panels' functions. What C6002EH has is a traditional Combi control-panel (CP), identical to the other C-Series models and comprising the normal ON/OFF switch, room-temperature selector and mode selector (water only, hot-air + water, etc). The 2nd panel is, in fact, merely a Power Selector Switch (PSS) controlling which 'fuel' the heater operates on - 230V-only, gas-only, or ("mixed") 230V + gas. With C6002EH, you first select (via the PSS) the power-source you intend the heater to use, then choose (via the CP in the time-honoured way) what you want the heater to do. I asked what happened if you selected a power-source that wasn't there (like a non-existent 230V supply). "The heater won't work," was the reply. This greatly increased my confidence as I had feared 'smart' circuitry might have been used similar to that of AES fridges (a particular bete noire of mine). However, I continue to think C6002EH will cause the Truma guys hassle. After 2 exposures to it, asking lots of sceptical questions and begging an Operating Instructions leaflet, I now understand the principles behind the thing. But I'm still not 100% certain exactly what happens in practice when the heater runs in "mixed" 230V + gas mode. And let's not forget I'm a very (and sometimes bitterly) experienced Truma Combi user. The fun will surely begin as this heater finds its way into leisure vehicles as standard fitment. Can you imagine the how-to-use-a-C6002EH explanation newcomers to motorcaravanning will get at hand-over time and the hypnotic trance this will induce? I don't think I'm being unduly pessimistic, so I reckon there's a future niche for me as a vastly over-paid roving C6002EH guru. Or maybe I should set up a premium-rate telephone help-line ("Baffled By Your Truma C6002EH Heater? Ring Doctor Derek NOW!!!") The more I think about this the more cash I predict would roll Chez Uzzell-wards. Just for entertainment value, it's interesting to compare (German) Hobby prices and (UK) Eura Mobil prices for the same Combi heater upgrades with Truma's UK recommended retail price-list. To make matters simpler I've brought everything into Pounds Sterling, allowing £0.70 per Euro and normalising VAT at 17.5%. These are catalogue prices for the extra costs involved in (A) going from the standard gas-only C3402 to a gas-only C6002 and (B) from a gas-only C6002 to a gas/230V C6002EH. (A) - £167(Hobby), £195(Eura Mobil), £157(Truma) (B) - £188(Hobby), £306(Eura Mobil), £267(Truma) This makes the choice of a C66002EH in a Hobby almost a bargain, as not only does the heater option seem to be well priced in comparison to gas-only models, but there's extra work involved during an EH's installation that needs to be allowed for. Or perhaps I'm still trying to justify my decision to get one!
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I'm surprised you havn't been snapped up already by one of the motorhome mags for a 'Doc Derek' technical problems page.(MHM could do with one)I'm off soon for a few days in the FFB so I'll be using the heating again and trying to get to the bottom of why there's just a bat's breath of air coming out of 4 of them, whilst the two others are belting it out. Thanks for your help.
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