Hi
I am a DIY homeowner, I installed pex pipe in my garage floor 4 zone loops. I dont have gas so I am using an electric water heater to heat the water. I have the zones connected to a manifold, a 3 speed circ pump, pressure reducing valv and double check on incoming water supply, expansion tank near water heater and check valves on the circ lines. I also have a combo temp/pressure gage on supple and return loops. the supply loop is 120 degrees F return loop 110 degrees F on low speed. My problem is the normal pressure of t he system when pump is not running is around 40 psi. when I run the pump the system pressure climbs to where it exceeds the readings of the guage and pegs at the center of the temp gauge.
What do I need to do to control the pressure in the system?

Thanks
Duane