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Hi all, we have a 2009 Hymer B675 SL Bestline with electric floor warming which works on electic hook up only. This has stopped working and I'm after some advice as to where I can further my troubleshooting. So far I have:


1) Ascertained that all other 230v dependant appliances are working.

2) Checked the Elektroblock (EBL 101 C) for a specific named fuse - none found.

3) Checked the fuses for all the used "Reserve" slots - all seem fine.

4) As the rocker switch for the heating is by the wardrobe above the boiler I have had a good poke around in this cupboard. All I can find is the step relay and the consumer unit and about eleventybillion blocks of wires running from that in blocks, (All look like original factory fitted wiring) but no obvious fuse.


Can anyone help troubleshoot this issue or if you have this model van with this optional extra can you shed any light on any pre-requisites needed for this to work.


Additional information: The floor warming was working perfectly prior to having some 12v sockets installed. These sockets were wired into the Elektroblock I understand, however, the company who installed them maintain that nothing else was disturbed and that what they have done should have no impact. They are at a loss as to why it no longer works.


Any help gratefully received but please be mindful that the above is pretty much the limit of knowledge of the dark art of electronics so please, if you are replying, keep it nice and simple! (lol)

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There are a few on-line references to the 230V floor heating system that Hymer used to offer, with one comment saying that the system included a large transformer that reduced the 230V voltage to 60V.


As the system is only operable when the motorhome is connected to a 230V hook-up, the first thing to check would the motorhome's mains distribution unit to see if there is dedicated circuit-breaker for the floor heating system. However, owners of Hymers with this option generally seem to have little knowledge of the equipment involved or how to trouble-shoot the system.


I'm guessing that the system fitted by Hymer would be pretty simple and similar to the Rapido floor heating discussed here



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I would expect your floor heating to be powered at 230V from EHU.


You mention checking fuses on the Electroblok which handles 12V supplies, It is possible that any temperature control could use a 12V supply.


However the power supply will be at 230V via the mains consumer unit, which you only mention casually.


May I suggest checking the consumer unit for informative labelling, and possible MCB. (I assume that you are checking while on EHU.)


The only part of the installation that could be electronic would be the thermostat, and any timer unit. The remainder is simply electric, as defined by not containing an active component, e.g. transistor, or IC.




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Hi, Derek, thanks for that.


I am one of those Hymer owners you mention which have little or no knowledge of the equipment we have or how to trouble shoot them. For our part, this is due to the fact that we have purchased a 10 year old van, which has most manuals but there doesn't seem to be one for the underfloor heating. Perhaps one wasn't available at the time of purchase.


Also, I am unable to do anything further than rudimentary trouble shooting due to the fact that I have little experience in anything to do with electronics, hence my question penned to this forum (lol)


I have read the posts you kindly provided a link to but it doesn't really tell me anything useful. What does sound useful is the comment you mention from your first paragraph regarding the transfer reducing the power. Are you able to post this link? Any google searches for Hymer underfloor heating that I have read so far have not mentioned this!


Thank you :-D

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Thanks for your reply Alan. There is no information on the consumer unit sadly, but to confirm, yes I am checking whilst on 230v.


I'm going to take a closer look at the electronics locker to see if I can gather any more information.




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Our van came with such a system and there will most likely be a transformer i.e large(ish) box used to step down from 230V to a lower voltage, so 60-40V. You should hear humming when it's turned on. I wouldn't expect it to be wired from EBL as it has nothing to do with 12V system. I have no idea where it might be located in a hymer.
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Dill - 2020-02-01 3:12 PM


...I have read the posts you kindly provided a link to but it doesn't really tell me anything useful. What does sound useful is the comment you mention from your first paragraph regarding the transfer reducing the power. Are you able to post this link? Any google searches for Hymer underfloor heating that I have read so far have not mentioned this!


Thank you :-D


The reference to a “big transformer” was in this 2010 MHFacts discussion




This is what was said


Our Hymer has underfloor heating, it runs on mains (actually dropped down to 60v through a big transformer) and whilst it isn't enough to heat the van on its own it does make a huge difference to the comfort, especially when you first get up.


I’ve looked for better information on German and French websites, but with no real success. It seems that this type of floor heating has been offered quite widely in the past as an option for German-built caravans, not just for motorhomes, but I haven’t been able to find any ’technical’ details. This enquiry from a French motorhome forum refers, but no advice was forthcoming.


I have a problem with my heated floor.

I have a 2007 HYMER B 660 SL Integral, bought second-hand last year.

In February 2017 we went to the snow in Les Angles (66).

The heated floor worked very well (pleasant in the morning barefoot)

Currently it does not work. I looked at the manual which talks about a 10A fuse. In the side compartment above the cell batteries I found a 10A fuse which I changed for safety, but it's the same. I specify that the yellow light of the switch works.

Is there another fuse elsewhere?

Can anyone help me ?


The enquiry mentions the operating switch illuminating yellow - did your switch light up and, if so, does it still do so?


You might try seeking advice about this on other UK forums (MotorhomrFacts, MotorhomeFun, etc.) as there may be a Hymer owner somewhere who has intimate knowledge of the floor-heating system. Or try the Hymer Club UK Facebook Group




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Thank you all for your replies.


It turned out to be a simple fix. When the 12v sockets were installed, the inverter was turned off. It would appear that the underfloor heating cable runs into an 'Inverter input' socket of a waeco - power accessory unit. The unit has 4 ports, a standard EU plug socket named 'Out B' which is currently free, another one marked 'Output A' but not sure what is plugged into this, and 2 different plugs marked 'Inverter Input' and 'Line Input'. The latter is not in use. Not sure if this is how the underfloor heating should be wired as it would seem to my uneducated brain that it really shouldn't be dependent upon the inverter?

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Thanks for the feedback.


I’m guessing that the Waeco unit is not an inverter as such, but a ‘mains adaptor' an example of which is here




That particular Waeco product provides a 75W/25V DC output, but the unit you have may well be different.


(Can you tell from your unit what its Waeco reference number is?)


Anyway, the ‘mains adaptor’ acts as a transformer, which would make sense for a low-output floor heating system.

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Hi Derek, thanks again for your continuing support and informative responses.


I have taken a further look at the unit but sadly all the writing that I am able to see is Waeco Perfect Power Accessory but no other identifying marks are visible. As an aside but this may help, we originally had a waeco SinePower SP1500 but this was replaced by the dealers under warranty as it didn't work. Unfortunately they didn't replace it with like for like in so much as its not a Waeco but a sunsloar one, so not sure if this makes any difference or not! :-S


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What you have is the unit shown on this advert and on the photo attached below




GOOGLE translates the advert’s description as follows


WAECO PerfectPower Accessory; Priority switching for all inverters up to 2300 watts even when used with a roof air conditioner


the priority circuit is intended for voltage distribution in vehicles with two possible power sources. If there are two 230 volt voltages on the device - a landline voltage and a voltage generated by the inverter (vehicle battery) - the landline voltage is used primarily. This ensures that the limited power supply from the battery is not used unnecessarily. The priority circuit can be used for all inverters - even for existing ones - up to an output of 2300 watts. The device has a second socket for use with a roof air conditioner, as soon as the roof air conditioner is running, the second socket is switched off

Input voltage: 230 volts AC

Output voltage: 230 volts AC

Output frequency: 50 Hz

Continuous load capacity: 10 A.

Output power: max. 2300 watts

Dimensions (WxHxD): 190 x 80 x 80 mm

Item code: Priority circuit for WAECO inverters

Scope of delivery: priority circuit

Delivery including cables

Item number: VS-230-2-K

Factory sales special device


Not sure how it dovetails into the rest of the Hymer’s electrical system, but from what you’ve said it appears to sit between the inverter and the floor heating system and, consequently, turning off the inverter would prevent the floor heating from operating.



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OMG Derek, you are so helpful, thank you so much. This all makes perfect sense as we have an air conditioning unit too. I spent quite some time googling this, but admittedly the UK site.


I can't thank you enough.


Cheers :-) :-) :-)

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Honestly puzzled by this... Why is the floor heating wired to waeco inverter input rather than output?


Or, is the inverter (lower priority) input actually EHU and the output is then the floor heating? Easily tested by swiching from inverter input to line input. Still doesn't explain the AC and inverter and why those aren't plugged into Waeco unit.

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The Waeco unit fitted to Dill’s Hymer has a Part Number reference of VS-230-2- K. I assume that the “2” relates to it having two output sockets as there is a single output socket version referred to as VS 230.


The VS 230 unit is described here




and that webpage permits an Installation and Operating Manual .pdf file to be downloaded. (The relevant information is attached below).


The VS 230 unit’s operation is straightforward - there is a socket for 230V input from an inverter, a socket for input from a 230V mains supply, and a 230V output socket. If the inverter is providing 230V power, whatever is connected to the unit’s output socket will run from the inverter. But if the unit detects a ‘live’ 230V mains supply, it will switch the output so that the mains supply is used rather than the inverter’s supply.


In Dill’s case the “Line Input” socket (230V mains supply) is not connected, so the unit will be accepting 230V power from the inverter and just passing that on to the output socket without any switching taking place. If power for the Hymer’s floor heating system comes from the Waeco unit’s output socket and the inverter is not switched on, the heating clearly would not operate - but that would not prevent there being a transformer between the Waeco unit and the floor heating system to reduce the 230 voltage.


Dill has said that the Waeco SinePower SP1500 inverter that was in the Hymer was replaced, and this MAY have caused the Hymer’s original wiring to be modified. In principle, if the inverter is providing 230V power to the Waeco unit and the Waeco unit is passing that power on to the floor heating system, the floor heating system should be operable from the Hymer’s leisure battery - but Dill has said that the floor heating system only operates when the Hymer is connected to a 230V electrical hook-up (EHU).


As far as I can see the Waeco unit is doing nothing productive - though there is probably a fuse in it that might be useful - but it would be necessary to examine the Hymer’s complete electrical system more closely (including the air-conditioner wiring) to decide what’s going on.


At least it’s now known that the inverter needs to be switched on for the floor heating system to operate, though I’d want to check that the floor heating system does indeed only work when the Hymer is on EHU. If the floor heating will work from the Hymer’s leisure battery when that battery is not being charged, there’s a real risk of the battery being ‘flattened’.



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Exactly what I don't understand :-D If floor heating is wired to inverter via waeco inverter input then it doesn't care whether there is EHU or not. It would work regardless. It will likely flatten the battery within hours but it should work.


But if the lead going in waeco inverter input is actually EHU then things start to make sense. In which case the inverter and AC are on a completely different circuit and have nothing to do with waeco unit. This "theory" is easy to test, just by switching the lead from inverter input to (correct) line input.

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The Waeco VS-230-2-K unit can accept a 230V input from an inverter and a separate 230V input from a mains power-supply. The unit prioritises on the inverter source and swaps to the mains power-source only when the latter supply is recognised as being live.


Dill has said that the floor heating system only worked when the motorhome was connected to a mains hook-up. It was noticed that the system no longer worked after extra 12V sockets had been installed in the motorhome. It has now been discovered that the inverter had been switched off when the 12V sockets were being installed, and switching the inverter back on has resulted in the floor heating system functioning again. So, however the Hymer is wired, the inverter has an effect on the floor heating system.


Dill’s photo seems to show that the inverter is installed adjacent to the Waeco unit. If that’s correct, then it should be straightforward to confirm whether the black cable currently plugged into the “Inverter Input” socket leads directly to the inverter. If it does, then it’s understandable why switching off the inverter would cause the floor heating system to stop working. If the black cable were an ‘EHU feed’, then switching off the inverter should not stop the floor heating system from working. (It would be worth checking whether there is another cable ‘loose’ near the Waeco unit that might lead back to a 230V mains power-source.)


As you’ve said, the present wiring suggests (assuming that the white cabling that’s plugged into the “Output A” socket leads to the floor heating system) that the floor heating system will be powered from the Hymer’s leisure battery and be operable even when the Hymer is off EHU. I suppose there might be some sort of ‘interlock’ to prevent the inverter from operating unless the motorhome is on EHU, but that would be odd too.

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Hi, thanks for your reply and apologies for the delayed response. I have switched the lead from the inverter input socket to the line socket as requested. The underfloor heating will take a while to kick in so will post again a little later, however, this may be a moot point as the air con unit is now not working on EHU!
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Hiya, a little bit further investigation! I am assuming that this large white box under the seat, directly above the 'electrics' locker is the underfloor heating transformer you have mentioned? The reason for the assumption is that when the underfloor heating is on it gets hot, although I appreciate this may be co-incidence! It has a brown and a blue wire coming from the back. The front is clear to see I believe.


To the right of this are 4 x brown and 4 x blue cables, These are then covered in pairs (blue/brown) in black cabling sleeve. One of the pair appears to be the set that runs to the back of the big white box.



To the right of the picture:

The Round white ish unit with the thick white cable running into it is the 'inverter' output 230v 3 pin socket.

The remote unit for the inverter is above it with a black cable. The flattened black cable would appear to be for the inverter remote.

The 2 x 2 usb 12v sockets are above this and use the other black cables (one to each).


I am going to poke around in the 'electrics' locker again to see if I can provide some further information :-)


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As the large white box gets hot when the floor heating system is on, there’s little doubt that the box is the transformer that’s been mentioned above and elsewhere.


When you've turned on the floor heating system in the past, did you always connect your Hymer to a 230V EHU first, on the basis that you ‘knew’ that otherwise the system would not function?


The reason I ask is that I’ve wondered from early on whether the 230V AC power for the floor heating system and air-con unit was coming from the inverter (that was being powered from the leisure battery) and the leisure battery was not going flat because the Hymer’s on-board battery-charger was getting 230V from the EHU and providing 12V power to the leisure battery to keep it charged up.


(I notice that the Waeco SinePower SP1500 inverter was available with an optional remote control, and I assume the replacemen SunSolar inverter also has this...)

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Hiya, we actually did not know that we had underfloor heating when we purchased the van and at the handover we were told that the rocker switch was to turn on the electricity supply for hot water. We assumed that this just warmed the floor a bit too *-) (lol)


We later ascertained, having used a considerable amount of gas in a disproportionate amount of time, that neither the heating or the water worked on electricity! It was then that further investigation revealed the possibility of an electric floor warming unit.


I confess that I realise now that we have never tried it without EHU so will switch back the cable to the 'inverter input' socket as it was before, see if the air con works again, then disconnect the EHU and see if that works!


Whilst I have found a little quide to the optional remote control for the Waeco SinePower SP1500 we never found one. We only discovered that this inverter was not working when I asked the dealer to tell us how to switch it on and off. It was then that they confirmed it wasn't working and replaced as previously mentioned. They did fit an optional remote for us, but I'm not 100% sure that it is right, as even when the inverter is off the sliding power usage output led s go from zero to 100% on a regular cycle!


I have also since found another white cable in the 'electronics locker' which looks like it should be plugged into something but has later been removed? This is to the left of the Waeco Perfect Power Accessory unit. Pic follows:


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