Upon arrival unit was on and customer stated they had no heat to the downstairs area. Found the zone valve had 24v going to it and the end switch was closing causing the aquastat to send power to the circulator pump. Checked power at the aquastat and had 120v. Checked the circulator pump and found it had no voltage. Bypassed the aquastat and jumped the circulator pump and the pump turned on showing the aquastat is bad and not sending power. After getting customer authorization we replaced the old aquastat with a new one. Turned the unit on and the unit started working properly. Purged some air out of the basement zone. Started and tested the system. Had hot water coming back on the return for the lower section of the zone. When leaving boiler pressure was at 19psi