I just bought a home. Everything was fine during the walkthrough. But then one day I left the heat on while at work (so room could be toasty when I got home) and because it was at desired warmth (actually a little hotter), I turned it off.

Went back up to my room a couple hours later and the room was just as room. 

Long story short, the heaters continue to run even when the thermostat is off.

I live in CT, so I have baseboard heating. It is also a townhome. 

I cut the power and the heaters went off. But when I turned it back on (thermostat off) the heaters came back on. So I think it’s a thermostat issue. 

Attached are pictures of the thermostat I had and the one I just bought. 

My issue is that the new one I bought, the holder for it is bigger than the spot that currently exists. 

Any solutions? I am not a handy person. I dont mind learning but I am looking for simpler solutions that won’t necessarily have a great chance or failure. 

I was thinking of getting a slab of wood and cutting it to the size of the new thermostat holder’s size and maybe drilling a hole through it. Put it over the old spot and use that to mount my new thermostat and holder. 

I have not tried anything though. 

Any other solutions? 

I think the new thermostat I bought wont work either but that’s another story. On the honeywell thermostat hookup it has a spot for a red wire, yellow wire and white wire. But I have no white wire. Just red, yellow (at least it looks yellow) and black 🙃. However, at lowes, this was the only one I could find. 

I don’t have central AC so I just need a heat-controlling one. All of the other ones they had do everything. This was the only one that did just heat. 

How would you go about this?