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Eberspächer Combitronic heating/water system.


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I have an Eberspächer Combitronic system fitted in my Autocruise Stardream.

I am thinking I ought to empty the Hot Water Tank (Calorifer?) for the winter period to avoid freezing.


Which valve would I open to empty it please? I can see a red cap at the end of a valve with a blue pipe leading to it; and a black cap at the end of a valve with with a blue, red and black pipe leading to it. Would it be the red one? How far would I turn it, in which direction, and when will I know the tank is empty?


Where will the water drain to? My waste water tank?


Could I not just turn the hot tap on to empty the hot water tank? Where does the anti freeze attached to the system come into play?Presumably it can't enter the hot water supply?


Any help much appreciated. Thanks.



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Welcome to the Out&AboutLive forums, Duncan.


I believe the design of your Autocruise Stardream’s Combitronic system will be similar to that shown in the 1st file attached below.


Liquid containing antifreeze is held in the Header Tank. This liquid is heated within the diesel-fuelled Hydronic heater (normally housed in the motorhome’s engine compartment) and the heated liquid is then circulated through a ‘closed loop’ of pipework that passes through a Fan Matrix (for air heating) and through a Calorifier storage vesssel where the hot pipework heats cold fresh-water that enters the Calorifier through the blue water-hose shown on the left of the diagram. The heated fresh-water then goes from the Calorifier to hot-water outlets (taps, shower) through the red water-hoses shown on the left of the diagram.


A GOOGLE-search on "eberspacher combitronic draining” produces the following results




This 2013 MHFacts forum thread discussed draining a Combitronic system in an Autocruise motorhome




and says


To drain manually there is a red topped valve close to the tank (See picture) which you need to open half a turn and sometimes hold until the tank is empty.


I THINK the calorifier Autocruise used was similar to the one shown in the 2nd file attached below and that has a drain valve indicated by the red arrow, and I would have thought the water in the calorifier would just drain out externally rather than feed into the motorhome’s waste-water tank.


Cold fresh-water is pumped into the calorifier where it is heated up. Turning on a hot water tap (with the heating systen switched off) would just cause cold water to continue to be pumped into the calorifier to replace the water coming out of the hot tap. However, to allow air to enter the calorifier, it may be necessary (or advisable) to open a hot tap before opening the calorifier’s drain valve.


As water heating is via a ‘closed loop’ system, the liquid that transfers heat to the fresh-water in the calorifier should remain completely separate from the fresh-water in the calorifier and - provided that the effectiveness of the antifreeze in the heating liquid has been appropriately maintained - that liquid should not need draining during the winter.


There is an on-line Combitronic Operating Guide




but I’m not sure how relevant it will be to older systems.


I’d expect it to be practicable to drain the fresh-water from a motorhome with a Combitronic system so that the vehicle’s main fresh-water tank, calorifier, water-pump and hot and cold fresh-water pipework were all empty and, consequently, protected from potential frost damage. But I’d still anticipate being able to use the Combitronic heater to provide air heating. However, one difficulty is that Autocruise won’t necessarily have standardised on (say) water-hose colours (eg. you mentioned a blue, red and black water pipe).


You have not said how old your Stardream is, but I assume it was built before Swift subsumed Autocruise. It used to be possible to view on-line owner handbooks for ‘pre-Swift’ Autocruise motorhomes (that, hopefully, might have covered draining a Combitronic system) but I’m not sure if that can still be done.


You might try contacting an Eberspacher main agent near you (list in Combitronic Operating Guide) to see if they could help with the draining procedure, but it really needs somone with a degree of familiarity with a Combitronic-in-Autocruise system to see what your Stardream has got - and obviously that may be hard to arrange at present.


Another possibility for ‘draining’ advice might be to join the Autocruise Motorhome Owners Facebook group




(There was a compact version of Combitronic where most of the components were shoe-horned into a ‘box’ that was installed beneath a motorhome’s floor, and I believe Autocruise fitted that unit to some models. But if your Stardream has a separate calorifier, you don’t have the compact version.)



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This link is to an Eberspacher guide for a system wuth a calorifier




The drawing of the end of the calorifier (copied below) describes the fitting with the red knob near the base of the calorifier as a “Pressure release valve (PRV) and drain” and the fitting’s outlet is described as “To bilge”. It can be assumed from this that the calorifier drawing would be appropriate to a boat rather than a motothome, but draining via the PRV should be similar in both cases. (The Eberspacher guide does include instructions on draining the calorifier to guard against frost damage.)


As I said earlier, it’s normal when draining motorhome water systems (including draining the water heater) to let the water drain directly on to the ground, so I’d expect in a motorhome that the outlet of the PRV of a Combitronic’s calorifier would connect to a drain-hose that exits beneath the vehicle, rather than leading into the motorhome’s waste-water tank.


I’d also expect there to be another a drain-valve somewhere to allow the fresh-water tank to be drained and (perhaps) a further drain-valve to make draining simpler.


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