Honeywell RTH6500 WiFi Thermostat wiring questions for a heat pump
It looks like y1 on old one is Rc on the new one,unsure of this so satisfy yourself before trying connection based on this observation.Also have you noticed the link between R and Rc,I would question this.Try asking manufacturer of after market part for advice.STeve uk Engineer.The instuctions are poor and the terminal markings maybe wrong.with thermostat.com are mentioned for help.Sorry I   do not understand the istructions.I will sleep on it. Had another look,Must say may not be compatible. Honeywell surprise me,Action to take,do not know.I have not given up,but hold little hope for success.I am now checking my suggested connections before posting them.good question,too many combinations.Einstein had it easier. Respect STeve uk.L?Wire missing. Steve has been called many things,genius is not one of them.Steve uk.You are missing,Internal diagrams for the controller,and external diagrams for equipment to be connected to it,also cable overal diagrams. All factors to carry out  this project. I have touched on subjects relating to  this before and now have little to add.pn,System may have lv electronic control as well,consider this.Do not mix wiring.All parts of the system may need to be wifi compatible to use wifi controller.