Club 80-90 Forums

Standard propex thermostat. Works but it is too "coarse" in operation. You set it so at for example 5 degrees C it has "just" come on, you can even then back it off a bit till it is "just" about to go off. You then leave it on. The flippin van gets to about 20 before it turns off and then it stays off until it is well cold, only then does it come back on For the techie types this type of action is called Hysteresis. I have an almost new fan heater in my shed that does exactly the same.

Does anyone else's Propex stat exhibit this behaviour ?

p.s. - The stat is mounted in the usual position for a Hi-Top Leisure drive, next to the zig panel a bit to the right of the sink and half way up the side.

We have the same problem which we fixed by install a wife override unit. She now controls the temperature.

It's because they are a basic on/off stat. It probably requires a 2-3 degree temp drop for it to kick in again. You might find if you can get to the inside that there will be are adjuster on the little pcb, to make it come on with a smaller temp drop. But you will then probably post saying " my propex stat goes on/off to much"
Your best bet is to get a digistat that will run off 12v these have a 'anticipator' in them that keeps the van temp more stable. This though will always be a slight issue with a on/off heat source, ie doesn't modulate. For instance, I am in my van now, camped in a snow drift, I've set the rheostat on the ebber to number one. After the initial full power get the van warm stage, it now just ticking over and keeping the van temp very pleasant. No hot/cold phases
Oh, and if the fan heater in your shed does the same.... Is it 240v? If so does it have a seperate room stat? If so have you connected the neutral wire to it? (All room stats will work without a neutral, but the anticipator side of it won't, hence the hot cold cycles.....

Titus A Duxass wrote:We have the same problem which we fixed by install a wife override unit. She now controls the temperature.

Yep same here she switches it to max so it never goes off.

When my propex thermostat died I replaced it with a generic programmable timer/thermostat from b&q. Runs off a AA, which lasts for ages (1yr +). Forget the brand name but its a decent little thing, has an lcd display. Output is a tiny flip-flop relay so it uses no current.

Oh just checked lloyd's post. Whs..

syncroandy wrote:When my propex thermostat died I replaced it with a generic programmable timer/thermostat from b&q. Runs off a AA, which lasts for ages (1yr +). Forget the brand name but its a decent little thing, has an lcd display. Output is a tiny flip-flop relay so it uses no current.

I had wondered about getting summat like that. Do you find it is a bit more sensitive ?

The std one I have seems to have a on / off / on gap of at least 15 degrees C, literally. I guess it will be a simple bi-metallic strip type affair ? Does anyone know ? (just to save me going out in this weather and un-screwing it off the van )

Long overdue thread this. Will be really useful if we can create a 'how to' on this as mine is exactly the same. Its annoying actually as I can phone my van up to switch on the heating but without good control its a bit pointless.

CovKid wrote:Its annoying actually as I can phone my van up to switch on the heating but without good control its a bit pointless.

It's this weather that prompted me bringing it up. I too was going to fit a remote control "On" / "Off" to ours, though I was intending to use a key fob type thing.

ghost123uk wrote: The std one I have seems to have a on / off / on gap of at least 15 degrees C, literally. I guess it will be a simple bi-metallic strip type affair ? Does anyone know ? (just to save me going out in this weather and un-screwing it off the van )

It does have a thermistor in there (so it's a bit posher than just a bi-metalic strip)!
There is also a little potentiometer in there - which 'may' adjust the hysteresis ...... maybe !?!?

It would be an interesting experiment to see how long your van takes to drop, say, 5 degrees when the propex turns off - as making the thermostat more sensitive would need to be weighed against it cycling on/off every 2 minutes if the hysteresis was too small .... you'd almost need a 'variable hysteresis' dependent on the outside air temp and the thermal characteristics of your van !!

As I said above, a digistat has all this built in......

ghost123uk wrote: The std one I have seems to have a on / off / on gap of at least 15 degrees C, literally. I guess it will be a simple bi-metallic strip type affair ? Does anyone know ? (just to save me going out in this weather and un-screwing it off the van )

MidLifeCrisis wrote:It does have a thermistor in there (so it's a bit posher than just a bi-metalic strip)!
There is also a little potentiometer in there - which 'may' adjust the hysteresis ...... maybe !?!?

Oh, summat to do instead of spending hours on here, looking at the TV or staring out of the window at the snow / rain / wind. Will report back

MidLifeCrisis wrote:It would be an interesting experiment to see how long your van takes to drop, say, 5 degrees when the propex turns off - as making the thermostat more sensitive would need to be weighed against it cycling on/off every 2 minutes if the hysteresis was too small .... you'd almost need a 'variable hysteresis' dependent on the outside air temp and the thermal characteristics of your van !!

As mentioned, it currently drops at least 15 degrees before it comes on again, so making it "too sensitive" is likely an impossible dream

Will have look / play

@ Lloydy and anyone else who mentioned it, I am reluctant to mess about swapping the standard stat due to how it is mounted (don't ask ) etc... but I have not ruled it out

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I have ordered a wireless on / off device and will be fitting it ! Imagine coming out of the house in this weather and into a pre-warmed van

Some of us don't have to imagine!

Oldiebut goodie wrote:Some of us don't have to imagine!

Guess what I found, and here on 80-90 as well !

Propex Heating

Adjustment of Thermostat Sensitivity

The Adjuster preset is a hysteresis control which can alter the temperature differential from 4°C to 1/2°C.

To adjust the thermostat, first pull the dial knob off and remove case by undoing the screw beneath the knob.
The diagram overleaf shows the position of the adjuster. For maximum sensitivity turn the preset
fully anticlockwise, and for minimum sensitivity turn it clockwise. The preset is designed to be adjusted using
a small screwdriver. There is a small arrow in the centre to show which way it is adjusted.
The preset is not a linear control and most of the adjustment is toward the anticlockwise endstop.

From http://www.club80-90.co.uk/pages/downlo ... ompact.pdf" onclick="window.open(this.href);return false;

Not sure why mine seems to be 15 degrees of hysteresis when 4 degrees is quoted as the max
Now, where is my little screwdriver

Did it work?