Heater blowing cold when should be heating (2025)

My wife's C30 (2007 1.6d) has started blowing cold air in the mornings when it shouldn't as the temperature's typically been around 4C/39F and the dials are set to around 23C/73F so it should be heating and maintaining the temperature as she has a 40 minute commute. The car isn't garaged overnight. Thing is, it doesn't do this reliably in the mornings but more reliably does it in the evenings when she's coming home. With winter round the corner, it'd be good to get this sorted.

My plan of attack is to try the following based on what I learned in my old 2002 V70 D5 SE which developed its own quirky heater. Can anyone add anything to this before I take it into the local garage?

1. Hoover the little grid with the temperature sensor in it to try to clear it of fluff. (I'm guessing that's up in the middle near the cabin lights?)
2. Check the air inlets for blocks.
3. Turn the temperature dials right down to low then up to high a few times to see if it reverts to normal working.
4. Replace cabin filters (even though these were only done at service 6 months ago)

I'm surprised to have another Volvo with heater issues. This is 2 out of 2 now. I'm considering getting another V70 or XC70 for myself soon but I'm concerned that the heaters/climate control on Volvos generally could be a weak point - is this a known thing?

Is the thermostat ok? Engine temperature, once warm, stays warm (~90C)?

If the gauge doesn't stay at the middle of the scale, I'd replace the thermostat first.

Did you sort this out? My C30 is now blowing colder air on the driver side (LH) than on the RHS. If I put it on the highest setting, it seems to work fine, but as soon as I put it back to a normal temperature (e.g. 22deg) , I get cold on the left, and hot on the right.

Any ideas?

Seems solved by now:

I put the blower to min, so I could listen to the steppers move the flaps. I have put, sequentially, driver side, passenger side, both sides, first to "lo" setting for a few seconds, then to "hi" for a few seconds. The system must perform some kind of learning for the position on the steppers, and now everything seems back to normal.