Viessmann C code after install and commissioning

[eagleeye]

Installed a Viessmann combi on Friday and couldn't get heating working. Hot water fine but not heating. Had a letter C on the display. Reset it and it went through startup and then went to C again. Called Viessmann technical and even they didn't know what it was.
Has anyone else had this and if so what is the cause.
Thanks
[automerge]1590954543[/automerge]

[automerge]1591039587[/automerge]
Viessmann been there today and said that the installer wired it up wrong and blew the PCB and that's the C symbol

 

[Tarquin]

That's an 050 model. If you connect 240v to the thermostat connection instead of zero volts you will blow part of the display board up, resulting in either no display or a corrupted display. If your unlucky it will take out the main pcb too.
The thermostat connection is a naked terminal block fixed underneath the boiler, so any decent electrician should realise it's not a 240v connection you would hope.