Hello,

I have a hot water boiler and a Honeywell CT3500 programmable thermostat (just moved in). The heat works, but does not turn off even after the thermostat stops (10 degrees or so higher.. ).

I have done some research for the probable cause. The first one that I believe is not the case is a stuck zone valve (2 zone home). This does not appear to be it.
What I believe it to be is that it is an older, 3 wire zone/boiler, and that most thermostats are not compatible with it.

Any help is appreciated!!

Someone else had this issue recently, and hvac1000 produced a list of compatible thermostats. Hang tight, I'm sure he'll be around soon...

These thermostats from White rodger are compatable with 3 wire zone valves.

Model Number Programming Options Contacts Profile Terminals

1E35-910 Non-Programmable Sealed Mercury Cell Vertical 4, 5, 6
1F35-910 Non-Programmable Sealed Mercury Cell Horizontal 4, R5, Y6
1F90-371 5+1+1, 5+2 Electronic Horizontal RC, RH, W, Y, G, MV, O, B, +, S, -, 6
1F96-344 Non-Programmable Electronic Horizontal RC, RH, W, Y, G, MV, O, B, +, S, -, 6
1F97-371 7-Day Electronic Horizontal RC, RH, W, Y, G, MV, O, B, +, S, -, 6
1F95-1277 Touch Screen 7-Day, 5+1+1, or Non-Programmable Electronic Horizontal RC, RH, C, W/E, W2, Y, Y2, G, O, B, 6, L, +, S, -
1F97-1277 Touch Screen 7-Day, 5+1+1, or Non-Programmable Electronic Horizontal RC, RH, C, W, Y, G, O, B, W/E, L, 6, +, S, -
1F97-391 7-Day Electronic Horizontal RC, RH, W, Y, G, 6, HM1, HM2, S1, S2, S3
1F80-0471 5+1+1, 5+2, or Non-Programmable Electronic Horizontal RC, RH, C, W, Y, G, O/B

1F86-0471 Non-Programmable Electronic Horizontal RC, RH, C, W, Y, O/B