Whale blown air heater fault code reset

Hi
My Whale MK2 gas / electric blown air heater control panel is showing four flashing lights ‘ Combustion air fault’ and says to check both air inlet and exhaust flues for blockages etc. 

I have visually checked the flues and they seem fine and have released under them van to ensure the is no water trapped.

Does anyone know if there is a reset switch for the unit as after following the reset off / on sequence the flashing lights still persist.

TIA

I wasn't aware they used Whale heater back in 2012. My 2010 Sussx has Truma.

Definitely a Whale also have the Whale water heater. Neither have given us any problems since buying the van in 2013.

I was able to reset the heater by turning off 240v and 12v power and leaving it off overnight. It worked fine on electric but when used on gas only lasted about four minutes before cutting out and showing the four flashing red light fault code again.
Did use a vacuum connected to the end of the flues but no change.