I don't know if the Webasto is the same? My Espar did not come with the altitude compensation module. I could start the heater at my house (6,512ft) but not up in the mountains however if I started it at home and then drove up the mountain it would run all weekend. Fixed by installing the altitude module. On another occasion the heater wasn't starting and running reliably I suspected a voltage issue but it always tested to spec. I eventually discovered that a bolt on my shunt wasn't tight causing the intermittent fault. Connections are cheep and easy to find and fix, I should have started there.