Traumatic c6000 ,cutting out

My traumatic c6000 starts up, ignites and starts fan. After a few minutes it cuts out and red light comes on. I disconnected the electric dump valve as it had a leak and bypassed the piping. The dump valve is wired in but not piped in...I'm wondering does water need to be in dump valve mechanism for the start up cycle to work correctly as it seems the system is shutting down as a safety precaution?

@Hymer544

update in case it helps anyone else in future:
the auto dump valve does need to be connected to water for the c6000 to work properly. I had taken mine out due to suspected leak in the dump valve but left the wiring connected to control unit. I presume there was an interlock in the device that switched the heater off in case of tank being empty. I re-connected the valve and the device worked again as normal.