Aux/coolant/water heater draining my engine battery

[Super Californilistic]

Today I was told by the mechanic shop that the coolant webasto heater is draining my engine battery. Even when the engine is off and the car is locked, I can hear some fan working under the left front seat (under the van). In matter of 3-4 days the battery gets emptied. The shop is a small one and can’t fix it. Can anyone suggest what I could do?
All help is highly appreciated.

 

[dspuk]

None of that sounds like a correct diagnosis. Given it looks like you have a T7 Cali it’s under warranty, go take it to a main dealer to get fixed for free.

 

[Super Californilistic]

None of that sounds like a correct diagnosis. Given it looks like you have a T7 Cali it’s under warranty, go take it to a main dealer to get fixed for free.

Thanks for answering. I have Cali T5 2008. Unfortunately no warranty. Why do you think the diagnosis is incorrect?

 

[dspuk]

Thanks for answering. I have Cali T5 2008. Unfortunately no warranty. Why do you think the diagnosis is incorrect?

Because your vehicle listing says T7 it did not tally. With a T5 there are wiser heads on here than me to advise.