Alde Fluid Loss

Make sure that you have found and checked all of the bleed valves, our Swift was a devil for hidden ones lurking in wheel arch cupboards and behind seats.

When we had a header tank with circulating pump in the wardrobe, although there was no leak, the smell of the Alde fluid was always very strong in the wardrobe. Even so this level of "evaporation loss" was not enough for us to need to top up between services.

 I would imagine that if you were leaking 125ml a month into your living space it would stink of coolant.

So I think it is leaving the vehicle,

Check that the drain plug has been fitted correctly, I have no idea where that may be on your caravan but I am sure someone on CT will be able to tell you if you let us know the model.

It could be a leak into the boiler, a leak into the gas burner for example would leave the van through the flue, worth having a "system off" sniff around there.

I believe (and I stand to be corrected on this) that the coloured dye in the coolant is fluorescent so a scan round in the dark with a UV (Notes checker) lamp may prove useful.

Might be a silly question here, but what level are you filling it to. Lower level or max?

It should be checked when cold and be at the lower (min) level. 
The high (max) is the expansion allowance. 
Any fluid above the lower level will be discharged during use via expansion and the lever will return to the lower mark when cold.

The fact that you are losing a constant amount, would suggest that may not be a leak. 

A low pressure test done on the system should prove, if you think there is a leak. Your dealer should be able to undertake this, or contact Alde.

likewise any good Plumber/heating engineer could do this.

Many thanks Stephen, very helpful. I believe I have checked all available bleed valves and there is no sign of fluid dripping from the the drain valve and the workshop placed cardboard underneath to check for any drips. I have not noticed any smells but will try a sniff test including the flue. Presumably if dripping into the actual heater this would take place even when it is switched off and then evaporating away when the boiler is working. The caravan is a 2017 Hymer Nova 585

I chatted with an Alde technician and she felt there were two possible causes, either a slight leak or the original fluid (yellow coloured fluid used by Hymer, was breaking down and evaporating. 

Has the fluid strength been checked? 

Hi Freedom. Originally I filled it to the max fill line when cold and of course when in use the fluid rose about 15mm above the max. However the max line on the expansion tank is a massive 190mm below the top escape outlet  which could likely hold another two litres of fluid so plenty of reserve room for expansion. Certainly I have never experienced the level approaching anywhere near an overfill even when the heating is on. Also as the fluid drops it continues to do so way below the minimum mark. 

I understand the workshop did a pressure test but will get them to confirm

Many thanks

Easy T I think this is the next step I need to have done. I can see condensation in the form of droplets on the inside of the expansion/fill tank above the actual fluid level. I am not sure whether or not this would occur anyway if the fluid strength was correct but as stated the Alde technician considered it could that the fluid is breaking down.

I did have problems on a previous caravan at around 9 months old which was noted as likely low concentration of antifreeze. Dealer changed fluid and informed that the problem was still present Alde were on an annual closure and so the dealer asked if I would return the caravan when they could discuss the problem with Alde or would I be prepared to take the caravan to Alde dealership at the dealers expense, have a free service the following year for any inconvenience and they would pay my site fees. I chose that option and went down to Alde where they explained to me and the dealer by phone and e-mail why the heating layout was not up to strength and how to overcome. The fluid, after the dealerships work was just under 14% instead of 40% ( or was it more?). 

I told the dealer to forget the £8 for my EHU pitch at a nearby CL as I had had a lovely afternoon and enjoyed my visit to the Alde workshop. 

That sounds like a rather large header tank. The alde one is listed as 1.5litres

I am not sure I understand how fluid concentration can affect the level or lead to losses from the system.

Even the "broken down" fluid, if such a thing exists still can't get out of the system any more than fresh full concentration fluid can.