GeoffisPure: So I have a bit of an update on my heatpump issue (making the room too hot).

The heatpump has a function called "I feel" which I hadn't been using.  Instead of taking the room temperature from the sensor on the unit, it takes the temperature from a sensor on the remote control.  This works well and the unit stops and starts as needed.  The conclusion I've reached is that the sensor on the unit isn't working well.  When the "I feel" mode isn't on and normal heat mode is used,  the unit detects a lower temperature than the room is.  The unit stays on at full speed for much longer than it should be.

I'm wondering if the location of the heat pump (floor based, in the old fire place) is the problem.  If the chimney wasn't capped, could the cold air behind the unit be throwing off the sensors?  I wouldn't have thought so as the sensor is on the front of the unit (according to the manual).  I've also noticed that there is no seal around the inside walls.  It's mostly tight but has gaps in the bottom corners: Pic1 Pic2

Would appreciate any thoughts anybody might have.

The way how I see this - hot air at the top, bottom is colder.

If the unit is on the floor, you will need to set the temperature lower than what you want (it takes longer before the heat reach the sensor at the bottom). If the unit is high up on the wall, you will need the temperature slightly higher than what you want.

Now, that you find out about the sensor on the remote, you should really be using that to get more accurate temperature.

The gap at the bottom, I thought that was a bit of a poor workmanship - but it should still be sealed (did you actually feel any air moving in/out?).