Fuel Burner / pre warmer not working L322

I have a 2007 L322 Diesel with the optional Pre Warmer / de-ice
All was working fine but now garage have told me there was a low voltage error when they investigated the Fuel Burner, They cleared the message and said try again but still nothing.
New batteries in remote and green light come on remote when pressed.
any ideas, be nice to have it working before it gets colder !!
thanks

Somewhere in this link http://www.fullfatrr.com/forum/topic5923.html may be your answer, I only briefly looked but somebody mentions having to unplug the remote receiver to properly pair with remote. Yours may have lost comms, particularly if you can't hear the burner fan.
Also I believe the burner uses a glow plug for ignition, I wonder if that's ok?
I presume you have checked the burner fuse?

No experience of this personally.