Biler CH & HW Conumdrum

[Rumine1]

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 even though the C27 Programmer light is activated. After about 15mins it finally kicks in but before that you can here a low pulsing buzzing noise coming from the 3 way valve's actuator. The Hot water is very hot and cyl stat set @ 45-50 deg C.
Any ideas apart from changing every piece of this system?
for info: Grant 70/90 Euroflame, B.House model: Horstmann C27 prog/timer, Horstmann Z322XL 3 way valve; Honeywell L641 cyl stat. DAB pump and rads with TRV's.

 

[dcawkwell]

Need to use a multimeter at the programmer.
It is actually live when the 3 program is on for HW and again for CH.

If not programmer is at fault. If you have live from the programmer.
Fault it in the wiring/thermostats.

 

[Rumine1]

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 actuator. The override lever is in the AUTO position and when the actuator makes this noise the lever slowly moves across to the manual position. This takes about 5 minutes (should only take 20 seconds) and then the boiler and circulating pump start up..... Do you think that it could be the valve's actuator that is faulty?