SIME Super 90 wireless timeclock?

I've got a SIME Super 90 boiler in my workshop that we turn off Friday evenings and turn on Monday mornings to save wasting gas over the weekend. I want to fit a wireless timeclock to the system so that we have heat when we open on Monday mornings without running new cabling. Does anyone know a suitable one.
I believe I would disconnect the existing "Timeclock over-ride" switch and connect to those terminals instead. (The existing timeclock on the boiler is 24H only)
The reason I have doubts about using just any available timeclock is that the schematic seems to indicate it needs volt-free contacts as it is switching 24v AC, and a timeclock I looked at on the Web delivers 240v via it's contacts.