Problem with heating probes: the cause of the freezing tanks?

Now, if you’ve been following some of my previous posts you’ll know that we’ve been having some real problems with our fresh water tank and grey water tank (and associated pipe-work) freezing in these sub-zero temperatures.

On more than one occasion this problem has caused us to have to seek sanctuary at one of the few campsites that have remained open all year to make use of their hot water facilities. At best this has been a bit annoying, at worst it has caused us to curtail some of our mountaineering plans!

I’ve been a bit disappointed with just how quickly and “easily” the ‘van’s plumbing seems to have been succumbing to the freezing weather. And once the frost has entered the pipes it seems to take an age for them to thaw out.

Before we bought the AutoTrail ‘van we did recognize that certain models of ‘vans were more susceptible to freezing pipe-work than others. Basically, in terms of plumbing, ‘vans fall into two principal configurations: those with tanks that are under-slung below the ‘van chassis and those where the tanks and plumbing remain within the living area. The latter is often accomplished using a double floor construction (usually supplied by 3rd party chassis manufacturer “Alko”), with the tanks and pipe-work located within the double floor, which can be heated using warm blown air from the living area of the ‘van. This makes these ‘vans much less susceptible to freezing.

You find that many of the European models (Hymer, Knaus, Burstner, Adria, Dethleffs, etc.) employ this type of construction and are rated to operate in alpine ski resorts. However, as with many things in life there is a compromise to be had, and in this case we found that many of the European ‘vans didn’t offer as comfortable layouts, their kitchens were a bit more sparse or their price was too expensive. In contrast we really like our AutoTrail 696G’s accommodation area: kitchen, lounge, bathroom, bedroom and storage.

So, knowing that our AutoTrail might not be able to handle really freezing conditions we chose a couple of added options to bolster its cold weather performance. The first thing we asked for was that all external pipe-work be lagged as well as the under-slung tanks. Secondly, we asked for 12 volt heating probes to be inserted into the two tanks so that we could at least stave off the water from freezing a bit.

Since we’ve had the ‘van (18 months) we’ve never needed to make use of the heating probes until now. Over the last few weeks I’ve had them “on” constantly – or so I thought – but it didn’t seem to make much of a difference. Eventually, I became convinced that they weren’t working properly. So, when I returned to my parents place just before Christmas I borrowed my Dad’s voltmeter and went to investigate the situation.

Switches in place for 12 volt heater probes

The first thing that I tried was to see if I could get a voltage across the switches (one for each probe in each tank). You can see the switches (faceplate) in the first photo. The switches can be “opened” quite easily and I didn’t get any voltage across either one! The problem now was to try to diagnose where the fault was. I thought that this would be difficult to do as the wiring from each switch disappeared under the Truma Combination Boiler and presumably made their way through the floor and out to each of the under-slung tanks. The prospect of crawling under the filthy ‘van in the freezing cold was not too appealing … but there was nothing else for it.

So under I crawled and I immediately noticed two things:

  1. The so-called lagging around the tanks was awful: it was as thin as tissue paper and only the sort of stuff you would put behind a radiator to reflect some heat back into the room – no wonder the heating probes weren’t coping;
  2. With the space being so tight I wasn’t going to be able to easily locate the probes and trace the wiring back into the ‘van.

    Heating probe cables were tucked beneath combi boiler

However, when I went back into the ‘van it turned out to be much easier than I thought to diagnose what was wrong with the probes. I decided to trace, with my hand, where the wires from the probe switches went to when they disappeared under the combi boiler – I imagined that they would disappear into the floor. But oh no, instead they weren’t connected to anything. They were simply lying tucked under the boiler – with not even their cable ends stripped in preparation for connection to the probes in the tanks. I suspect that TyneValley Motorhomes, who sold us the brand new ‘van, started to fit the probes and then accidentally forgot to finish the job. I’m not even sure if the probes have actually been fitted to the tanks and simply not been connected, or if the probes still require to be fitted.

Heating probe switches from the back - not the neatest of cut holes!

In the past we’ve met Jonathan, one of the Directors from TyneValley Motorhomes, and so I’ll give him a call to sort things out. I’m sure that there won’t be any problem as TyneValley have always been really professional and were extremely helpful when we bought the ‘van.

Now we know why the tanks are freezing quite so quickly: no heating probes plus inadequate insulation. I’ll let you know how we get on when we contact TyneValley.

About Cameron Speirs

Born and brought up in the Scottish Highlands, Cameron, has been interested in outdoor pursuits since he was a wee lad. Over the last few decades he has climbed extensively in the Italian Dolomites as well as summiting the Matterhorn and several other 4000m alpine peaks. Closer to home he has spent many wonderful weekends mountaineering and biking in Snowdonia, Cairngorms, Glen Coe, Skye and Lochaber.
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