Vaillant Eco TEC plus F72 error.

!3mth old boiler, serviced last month.On Friday showed F72 error (flow/return sensor fault - replace), spoke to installer who said I needed to contact Vaillant as under 10yr warranty. Told Vaillant about error and they sent an engineer the next day. Before even looking at the boiler, when I told him F72 error he immediately said it wasn't a boiler fault but either the pump or a blockage in the return pipe and to call the installer or a plumber. He then lowered the front cover and pressed the reset button, the boiler fired up and has since worked. He then left. Should he have checked/replaced the sensors rather than than instantly blaming the pump or a blockage?
Any advice much appreciated.
Thanks MikeD

You could pull up D40 and D41 in the disgnostics menu and display the flow and return temperatures and see if they are plausible..
What model of Ecotec?