I have them on separate ss relays.
Heater relay provides power to one side of the heater contactor trigger and the pressure switch supplies the other side.
The pump relay provides power to the pump solenoid and when the pump runs it provides the pressure to engage the flow switch and we have heat.
I did it this way to have more control over everything.
But i have other problems.
after 4 or 5 hrs my temp sensors go offline (every temp is 32F) and things on the dash go “unreachable” even though the rpi is still able to be ssh’d into.
after I reboot, all is ok.
I have 3 dallas sensors and read a sketchy power supply can cause that.
so i grabbed the one i bought for my rpi 3 and testing that.