Gas Boiler check valve

Hello, I have a new 2 zone pinnacle boiler installed, the problem is that when you take a shower or have zone one on zone 2 heats up. I have had check valve replaced, and it worked for a few days then the pipes started heating up again without heat on zone 2 on? Any suggestions?
Thanks
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You need to describe the equipment. How do you get domestic hot water? How many zones total? Do you have just circulators, or combination of circulators and zone valves? Pictures would help

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