Truma ultrastore not igniting

[Chezan]

Morning all just arrived at port solent for the boat tomorrow and we are not getting any hot water the boiler clicks but stays on red so I guess it is not firing up.we have a 2015 Auto trail Navajo tried a number of times gas fire ok and reset the main control panel any suggestions please

 

[Clivefog]

Reset the heater, plastic flap covers the reset push button and LEDs, can't remember if you have to press it twice or hold it in for a few seconds.