A thermostat set incorrectly is the second most common cause of a Calgary furnace not heating properly — and the second simplest fix after the filter check. Two settings to verify immediately: the fan setting and the system mode. If the fan is set to ON rather than AUTO, the blower runs continuously and circulates room-temperature air through the vents at all times — including during ... https://www.purcellheating.ca/furnace-not-heating-calgary-causes-fixes-guide/