Underfloor heating not switching on

[Diyisfun]

Boiler is firing up on main heating.
When underfloor is called for nothing.
I'm guessing what should happen, is pump starts, divert valve activates & then Boiler should fire.
I'm guessing at fault with pump, am I on the right lines.

 

[Diyisfun]

I have just removed, then replaced the batteries in the programmer & it's fired up & running. So bit like reboot.
But would like to know what the sequence is.