tank heaters

going to get nippy next week. wondering about using the tank heater/s. on ehu is it advisable to leave heater on or not . presumably they are low wattage. please advise.
Doug.

Where do you plan to be camping? Even in the Highlands it's not forecast to be very cold - min minus 2 - and only that cold in the middle of the night? With a reasonably full tank, the chances of a freeze-up during that short a period of time should be very low, unless the site you're on is very exposed and it's windy.

Then again, if the van has them and you're on a site with unmetered electricity, why not use them? They don't (in the overall scheme of things) take a lot of power...

just thought with the tanks exposed to the elements don't want a disaster. my previous van had tanks between floors and no tank heating. thanks for reply.

Someone correct me if I'm wrong but I believe they only work if temp is below 2° and tanks need to be at least 25% full.

once switched on, do they automatically turn on and off. Paul is probably correct with the 25% quantity necessary. tricky one as minimum amount shown on cp is this. bit of trial and hopefully very little error! thanks for input. will report back.
Doug

From our Kingham manual, they turn on when the contents of the tank temperature (NOT ambient air temp) reaches 7° and turn off again at 18°.

It doesn't specify a volume of water just "liquid in the tank". You should have an isolation switch somewhere to turn off the waste tank heater if it's empty, leaving the fresh tank one on.

There are 2 different systems at play.  

First the tank heaters have a temperature sensor switch on them.  You can feel the lump where the two wires enter them.  As Weegie has said, the switch closes when the sensors drops to about 7 degrees or below and doesn't open again until it reaches 18 degrees.  

Second, for the EC700, power is only sent to the tank blanket sensor switch when all of the following conditions apply:

a)  The EC700 is not shutdown
b)  The tank heater is turned on on the EC700 CP
c)  The tank water level indicator shows that the tank is at least 25% full
d)  The EC700 external temperature sensor shows that the outside temperature in 2 degrees or below
e)  The engine/alternator is running, or, the van is connected to an EHU with the PX300 mains charger turned on

If a tank heater hasn't been turned on on the EC700 CP and the EC700 senses the tank is at least 25% full and its 2 degrees or below, an e-mail/SMS frost alert should be sent to the owner courtesy of AS Monitor.

A word of warning.  A couple of years ago I discovered my tank heaters had been incorrectly wired in the factory.  I suspect other vans are incorrectly wired but the owners don't know it.  The tank heaters are very low wattage and its difficult to feel their heat.  The best way of testing them is to disconnect the external temperature sensor from the EC700's PCB which makes the EC700 think its minus 25 degrees.  Then press crushed ice cubes against each of the heaters' temperature sensor switches to ensure the switches are  closed.  Then using a DC clamp meter on the DC feed to each heater detect when current is flowing using different permutations of the EC700 CP tank heater settings and with 25% water in either tank or not.  This takes a lot of patience and determination, especially as getting under the van is very uncomfortable.

If you are bored, plough your way through this thread:

https://www.autosleeper-ownersforum.com/t40487-tank-blankets?highlight=Tank+blanket

I will never use my waste water tank heater.  If there is the remotest chance of it freezing, I will keep its drain tap open draining into a bucket.  If the tank is 25% or more full, the heater may stop it freezing but it won't stop the drain valve from freezing.  

Only the fresh water tank heater is of any value but it will have to be well below zero and for a quite a long time before it will start to freeze.  If there is any chance of freezing I will not travel with water in the fresh water tank or use a pitch that doesn't have an EHU.