Why don't you just use the Webasto UK website to find an authorised service engineer closest to where you live? That's what I did and have used them for services many times since 2010 when I had my first hot system from PF.
From my experience the agent advertised by Webasto UK in Middlesbrough hasn't done Webasto repairs for the past 2 years. The guy who did retired and they haven't replaced him.
The agent advised in Durham talked the talk but when it came to the point of getting a unit booked in for repair they responded they would get back to me. Still waiting but I just knew at the time it wasn't going to happen.
If you find someone who has been in the repair side for years on the canals then you have a better chance of getting a unit repaired than we do.
There was a guy on Ebay offering a repair service for Thermo 90's. His charge was nearly £400 plus parts. May as well buy a new one for £1350 because your repair costs won't be much less than that. Ask Splash and Dash.