Pressure relief valve leaks after zone valve install

I have a Burnham series 2 boiler where the pressure relief valves seems to start leaking after turn the thermostat off or it reaches itso temptress. I checked the expansion tank pressure 15psi , boiler off pressure is 15 psi aswell. I've shut the thermostat off and watched the pressure climb to 30 psi and start dripping. This is after adding baseboard heat and zone valves to my basement. Any ideas? Thanks!