Heating left exterior mirror failed

Hello, on my trip to Switzerland I noticed that the left mirror was constantly slammed during tunnel crossings. Now after the hand wash (I am always too lazy to leather it – the car – after that) I noticed again that the water drops did not disappear, while the right one had been dry for a long time. My questions: – is there a security for it, which may be responsible? – what can be broken, what must be renewed, what does it cost? MFG Pluto P.S. Dieselchen used exactly 6.6 liters to 100km on the journey from Beatenberg to Wuppertal (exactly 700km). At changing speeds, sometimes even 180, long time 140-160. You can’t complain about that. Oh yes, PC information and later calculation are identical. Whether it’s Lambda that I’ve been using for a few weeks? P.P.S. Before, I drove 3 Swiss pass roads, always nice from about 700m up to 2.400m, and down e tc. Together with the AB ride it makes exactly 6.9 liters. I have the feeling that the older, the more economical, he will probably return fuel to me in 1-2 years after a ride with him