Circulators shouldn't cause overshoot/overhheat issues. They just ensure that all rooms in multistory dwellings receive equal heat.

This might be causing your issue - read down to section on heating cycles per hour. It's the digital version of the heat anticipator found on older mercury bulb stats. Cycles per hour/firing rate is different for gas or oil, forced air or hot water, high eff furnaces, etc. http://www.honeywellcentral.com/more...qs/thermostats