Heating zones on when they shouldnt be.

Hi all,



About 9 yrs ago I installed a new boiler system and used a Taco SR506 to control the 4 zones (3 heating and 1 indirect DHW). I greatly limit each zones use to save oil, where 1 is never turned on, 1 is only on at night and the other is only on in the evening. This entire winter I've been noticing that areas that do NOT have the heat turned on, are warm! At times when I found this I went to the basement to feel the pipes and it seemed that the return pipes at the end of the zone (that wasn't supposed to be running) were warm and the supply pipes were less warm. It was happening mostly on 1 zone, so  thought maybe my Watts 2000 flow check was stuck or defective so that when another zone came on water was pumped backwards through the supposedly unheated zone.



However now I've found it with other zones being warm when they shouldn't be so theres no way that ALL the flow checks (or thermostats) went bad at the same time. I can never catch it at the time - its usually in the middle of the night that my unheated zone suddenly gets warm!



Is this a known problem with the SR506? It worked perfectly for 9 yrs until now and I would think it should last longer than this.



Any help would be appreciated. Thanks,



CJ