Navien Boiler Over Temperature error

abineri

I have a Navien boiler feeding three loops of 3/4" pex to baseboard heating. I have added another radiator and about 200 feet of 1/2" underfloor pex to my system on the same loop. The pressure in the system seems to be higher than previously and I am getting a fault code of 001 (temp to high in combustion chamber). What might I have done wrong and how can I correct this situation? I have two circulators on this system, one on supply and one on return to boiler.
Many thanks for your suggestions.