Bourton water heater

L
MUNewbie again ! 
Loving our Bourton . 
When heating water ( electric ) on site the Eco setting is fine but water just warm which is to be expected . When we use Hot setting we always get some sort of error warning ( the latest being frost but 8 degrees outside ) off to reread manual - any short cuts ? Possible air in tank re whale pump which we are going to look into as we can’t quite get the system correct 
At lovely site in Moffat at the mo .