Found relief valve leaking due to expansion tank being full of water and over pressurizing boiler. Closed off all 4 zones supply and return. Removed water from boiler. Replaced expansion tank, air vent, and relief valve. Filled boiler back up and removed air. Opened up each zone slowly to remove any residual air. Ran boiler, zones hot, no drip at relief valve, pressure is good. System running normally.