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Thanks dcawkwell, Yes there is power on the Horstmann C27 controller when both HW & CH start up on the the prog. Other wiring is in order including cylinder stat. However when the CH prog starts up there is a low pulsing humming noise coming directly from the the Horstmann Z322XL 3 way valve's...

Hi everyone this is my first post. My boiler's HW is working fine with the Horstmann C27 2ch; 3 prog. But the CH only comes on with the first 2 of the progs. The 3rd HW prog calls 1 hour before the 3rd CH prog and that is where the problem is. The CH just will not cut in and fire up the boiler...