I had this same tick tick tick last winter here in Switzerland. Then the weather warmed up and I have not heard it again. But I have recently had two fault codes P0442 and P441 in the last month.
Can this valve be serviced?

 

Last winter I had the Fault codes but kept the tank full once they were reset, bought an OBDII scanner and reset when necessary. Then eventually I just had a new valve fitted. All my fault codes have gone.
But I have ticking again and no fault codes, so for the moment choose to ignore it as I assume it is working if there is no fault code.