service tech

Griff

Recently i came across an unusual problem with a ultimate boiler with two zones and summer/ winter hook-up. The original zone has a B&G circulator and is a mono-flow system with convectors. The second zone(which was added approximately 10 years ago) has a 007 circulator and has a baseboard loop on the second floor. The original problem occurred two years ago when the flow valve on second floor loop was passing, so we replaced the flow valve. The second problem occurred about a month ago. This time the expansion tank was full, so the tank was drained and both loops purged and both loops were heating fine. A third call was generated yesterday and we went out and for the third time the flow valve for the second floor is passing hot water. I again purge the loop but not finding any air in the loop and again both loops are heating fine. The expansion tank on this system is an original steel tank and both circulator s are on the return side of the boiler. Why is this happening?