I'm installing the rth230b on a 3 wire gas fired boiler. The wires are blue, red, white.
On the old mercury stat the blue and red wre on the same post. Anybody know how I should wire this one? Thanks! Mike

Not sure what the blue does. If it worked connected to the red before, try both on the RH terminal and the white on the W.

I tried that and it didn't start it. But, it actually worked the opposite. (go figure.. )
Thanks for your help though. I appreciate it. I'm still having a hassle getting the program to run right, all the time. Strange to be inconsistent. But, so it goes for $30, I guess.
Regards.