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Check the cycle rate of the thermostat. If you have fin tube radiators, it should be set for 5 or 6 cph, even if the manufacturer says differently for "hot water." When the manufacturer says hot water, they mean big cast iron radiators. If your stat isn't electronic, rather than cycle rate it has anticipator. That's the little dial inside with decimal points in front of all the numbers. For best temp control--no overshoot--match the anticipator setting to amp draw of the load (zone valve?). You can find the amp draw on the end of the zone valve. If the anticipator is set for slower cycling (e.g. 3 cph) you will get temp overshoot when the heat turns off, and your space will feel cold before the heat turns on.