Honeywell ST9100A 1 day timer 1 channel

[Treeworks]

Could someone please confirm whether the ST9001A only controls the hot water or does it also control the central heating (or is it capable of controlling both but can optionally be wired up to control either one)?

I am doing a preliminary investigation of some issues with my system
(unvented cylinder and system boiler). The boiler's hot water pipe splits into 3, supplying CH. HW and u/f heating (each of these controlled by a motorised valve).

I have seen the CH come on when turning the ST9001A on and also seen it working when the ST9001A is off, so am well confused!

The user guide only states it provides 'timing control for your central heating system', which suggests CH and HW, but then why would CH turn on when timer is off?

 

[Whitespirit66]

This programmer controls only one part of the ch system.

Starting with everything off, and pipework cold, turn the programmer on, and see which of the 3 branches from your boiler starts heating up. You then know what it controls.

 

[Treeworks]

Thanks WhiteSpirit, I'll try what you suggested.