My Monitor MZ25C condensing boiler provides hot water for a dhw tank and two heating zones. The tank's calls for heat are always satisfied quickly and without any boiler limit shutdowns. Zone 1 (Z1) comprises an old but well-functioning radiant slab: a concrete slab covering approx. 800 sf, with seven 1/4 in. copper subcircuits. No problems here either; the tstat is easily satisfied, the space is very comfortable, and the boiler never reaches a safety limit while satisfying a call. Zone 2 (Z2), which is unfortunately the main part of our house, contains two subcircuits of convector baseboards, which traverse parallel exterior walls of the house before rejoining in a common return line back to the boiler. (Parallel return? I forget the name of this circuit design.) After 7-12 mins. of a call for heat--just when they're warming up a bit, the boiler will shutdown on pressure (45 psi, it's correct limit). I can temporarily alleviate the built-up pressure by turning the manual pressure relief valve (comes on the Monitor package, along with the exp. tank, circ., etc.) and get a slightly longer run-time, but shortly thereafter the boiler's aquastat will shut it down, and it's the same story as with the pressure shutdown: Short-Cycle City. By the way, it's not the temp. limit switch shutting down on temp, because the boiler would not re-start after a TLS shutdown without my depressing the manual reset button. But it's never necessary: the boiler will short-cycle just as quickly and badly after a temp shutdown as with a pres shutdown. Why is the aquastat shutting it down on temp, anyway? I thought its job was to maintain the boiler's supply at setpoint, not turn the boiler off the instant that it achieves it. I feel stupider by the minute. I bleed the baseboards regularly, hoping to relieve the pressure, but I never get more than a faint hiss of air. I've been through the crawl space looking for a possible problem with the supply/return lines of Z1, and in fact did find a stuck drainage bibb that the installers blessed me with, but replacing it had no effect on the pres/temp shutdown issue. My gut insists that the pres/temp issue is not physically in Z2, rather it is in the boiler package or possibly in the primary/secondary manifold that distributes boiler supply water to Z1 and Z2, and is only elicited by Z1 conditions. But I can't justify that hunch, much less diagnose and correct the darn problem. I'm just stumped. I would be very grateful for diagnostic assistance from the experts here.

I have a Dunkirk Empire II boiler, oil fired with a Beckett AFG burner. The water limit is set on 200 high and 170 low. I can use the hot water without mixing with cold and put my hand right under it, it's not hot enough. What could be wrong?