Yes, you need the expansion tank on the water heater. Where we're located, the check valve into the house is not required and the heated water can expand back into the well pressure tank. But, if you have a check valve on the water line as it enters the house, you're preventing any expansion back to the well pressure tank and you need the expansion tank at the heater. Most exp. tanks are pre-set at 40psi. I'm sure many here would change depending on the pressure switch settings at the well equipment but not me, I'd leave it at the 40, it'll do it's job.