what programmer or timeswitch.

[dlt27]

Hi my dad has just had a woodburner with back boiler fitted. It is the yeomans cl8 fully pumped system. I need a 2 channel programmer or timeswitch that has a common connection on the c/ heating and hot water. The reason for this is that a low limit stat has to be satisfied before the pump can come on. So I was hoping I could take a feed from the perm live to the low limit stat then a switch live back from the stat to the commons of the heating and hot water. Could anybody give me a model number of a timeclock or programmer that would be suitable because the ones I have looked at have the lives to the commons built integral to the unit so can't fit a stat between perm live and common.
(ps I'm an electrician who doesn't have a lot of experience with c/heating.) Thanks in advance.