I have a 2 wire (Red & Yellow) system for my boiler with no AC. I have put the red wire in the red slot and the yellow in the y slot. No luck. Am I wiring this incorrectly?

Do you have a display? Is it set up? What stat did you have before and why did you change it?

https://www.manualslib.com/manual/256949/Honeywell-Programmable-Thermostat-Rth6350.html?page=15#manual

Hi Morkstall

In most cases where there is a simple two wire thermostat for heat only you install one wire to R and one wire to W... color of the wires does not matter. Try installing the yellow wire to W... should be al set after that!

Mark