We have had the same basic issue a few weekends back: when having the heater on without electrical hookup, it stopped after about 1,5 hours and would not start again. Whereas before in the cold we happen to have been on hookup always, and it would go the whole night.
When we let the engine run a few minutes, it would start again, but then again stop quite soon. The moment the first few rays of sun hit our collectors on the roof the next morning, it would run again. While there are reports on the web where the heater would go all night when just on batteries.
We have researched the web extensively, and found FOUR possible reasons for the heater switching off too early when on battery alone. They are independent, so one can suffer from each four of them, and they are all worth checking when you have these kind of heater issues:
- the earth shunt problem, as discussed above and elsewhere on the forum.
- simply the batteries being old, and no longer having enough power (dûh).
- the threshold switch-off value in the board computer. Not so obvious. It turns out a certain series of Cali's had that threshold value programmed in at a higher voltage then before and nowadays again.
- the smaller battery fuse. We have two leisure batteries in the Cali, one has a fuse of 80A (quite adequate), the other of 50A (just barely enough). Quite often, it seems, the 50A fuse goes, but you don't really notice: your leisure system still goes, but you think you have two batteries where in fact you have one. So, only half the power you think... Especially when the power goes down quickly when not on hook-up, this is worth checking...
Ad 1: As that can also cause other erratic behaviour, we have ordered the earth shunt repair set from the german forum, and have built it in last Sunday. Already found the lights no longer flickering when the heater started up, and indeed the heater ran to 0,5V drain further down than before, and it didn't switch off (did not have the opportunity to let it run until it switched itself off and see how far down it would go now).
Ad 3: Ours is in that series, so we need to check this. We have found someone with the software to look into this, and indeed saw that a fault was registered where the heater had switched off because of the battery voltage dropping below the threshold level. But with that version of the software we couldn't check or change the actual threshold value. Still looking to find a Dutch forum member who could help us there.
It is register 0B (aux heater), record 08 (threshold value). The value in there used to be 153, meaning that the heater would switch off when the voltage on the leisure circuit would reach 9 + 1.53 = 10.53 V. On the german forum one can find many reports where people have found their Cali's have higher values programmed in, and they lower it to 153 again.
The forums say VW set that value higher to try and mitigate the aux heater/earth shunt problem. Once the earth shunt problem is fixed, it seems you can safely go back to the lower value. In newer Cali models it seems VW have fixed the earth shunt problem, and the value is lowered again. Not my wisdom, here I am just repeating what I have read.
