Pressure doesnt trip the Bosch water flow does. It also wont trip on a
drip or a trickle flow, it takes apx 1/4 gpm. I say the toilet is hooked
to the HW line. I bet its only when the toilet is flushed, open a few
cold sinks at the same time, I bet nothing happens to fire the Bosch,
there goes your pressure theory. The volume needed to start tankless are
a drawback for trying to get minimal water flow and saftey against drips
and such. Try yours at a minimal HW sink flow it should not start.