Just installed a weil-mclein ultra 155 bolier in my house with my neighbor who is a plumber. We got it up and running BUT, I'm am using 2 circulators for 2 zones with 2 thermostats, no domestic hot water. Manual fairly unclear about this setup. We can get it to run with 1 thermostat for 1 of the zones at a time. I think it has something to do with the priority settings, and where the thermostat wires are plugged in at. Also, possibly the timeout setting for circulator 1 when not being used for dhw.