Broken thermostat

[WeWereInParis]

We have a thermostat on our wall that controls our central heating (just a normal thermostat, not a hive type smart thingy). I've noticed that for the past few weeks it's been showing the wrong temp for the room - the temp it shows varies but never goes below about 44 degrees so is obviously massively out.

Does it need replacing? Is it the kind of thing that can be fixed? Do I need a professional to fix it, and if so, what kind of professional? Electrician?

Have you checked if it has a battery in it? I was surprised to learn our hardwired ones do. Batteries were dead. I couldn’t even see an obvious opening for it!

Hmm no I haven't. We've lived here 4 years, but I don't think we've got a manual for it. Luckily the actual central heating timing settings are pretty intuitive but I don't know where a battery might go.

I've had a look and there is a bit that looks like it should maybe open up, but I think I just nearly broke it trying to snap it open!

There are batteries! Which I've just replaced but it still says 45 degrees. I'm hoping that's just because I've only just put new ones in and it needs a few mins to get an accurate temp. I'm off to bed so hopefully when I get up tomorrow it will be correct.

Thanks!