If your owb is plumbed straight into your oil boiler without a heat exchanger, that is your problem. Zone valves can only stand so much slam from the volume and pressure from the owb. I had the same thing happen to me after 2 years from the dealer installed startup. Dealer said I would not need an expencive heat exchanger for my install to work with a 2 story. He was right, it worked great for a couple of years then I ended up replacing 5 zone valves and adding a plate exchanger. Hope this helps.
Just another point, I had a 007 on my oil boiler and an 0011 on my owb