System:
Boiler Worcester Danesmore 15/19, Honeywell 2 wire tank stat, Honeywell DT90 roomstat, Drayton Tempus 7 controller And Honeywell sundial wiring centre.
It's wired C Plan ( gravity HW with 2 port valve, pumped CH)
Problem:
I guess the issue is either the programmer wiring or the valve...