yes i agree with you, BUT if HW is OFF at the programmer, there WILL be power to the grey wire anyway.
If the programmer is faulty, and no power to the grey then you will be getting hw and heating!!!
Go to the start of the thread and read heating only.
Then read down to where it says no 240v power on the grey.
What do you suppose the problem is.
I'll give you two choices to make it easier.
Cylinder stat or programmer.