Hi all, looking for a little advice or an explanation as this is just weird

For about a week now I have had very little heat through any of the vents. The air flows fine, all the fan speeds work perfectly and the A/C is freezing cold.
The only way I have been able to get a tiny bit of luke warm air in is to set the face vents wheel all the way over to the red and the select them via the push button. Loads of air but barely warm.
Checked the coolant - al little low so topped up but made no difference
was thinking thermostat, as RRUK had suggested too
but.... Just now I hopped in the car with the spare key (not used it before) and the air came on instantly and HOT! this is great news but I have no idea why?

Any one have any ideas? thanks 2006my v8 vogue
Ktm superduke 990

Could still be a thermostat issue with an intermittent fault? failing that wiring or intermittent matrix issue? It's a funny one but luckily summer is just around the corner

Personally I'd see if the fault develops again and then start by changing the most likely/easiest/cheapest issue first.

thanks StevyD, its going to an indy for an oil change and gearbox oil change next week so while they have it Ill ask them to change the thermostat.
Ive not been to bad up front in the cold snap. The heated seats and wheel have been great. My 3 year old has not been so happy in the back though - keeps requesting we take the mrs Fiat 500 as its warm.. Think the cold is making him crazy  2006my v8 vogue
Ktm superduke 990

Sticking stat Discovery 4 HSE
1998 110 TUM HS FFR Hard Top XD WOLF
1982 Series 3 Hard Top
1998 90 TUL FFR Hard Top XD Wolf
1993 90 Tdi

*Gone: L405 4.4 VSE, L462 D5 HSE LUX, L663 Defender 110 HSE, Discovery 3 HSE, 2014MY Range Rover Sport 5.0 Supercharged AB Dynamic; L405 Exec Vogue SE 4.4, 5.0 Supercharged Autobiography, Defender TDCi XS CSW, Defender TD5 HT, Vogue SE TDV8, Vogue TD6, RRSport SC 4.2V8, Classic 3.9 Vogue Auto, Land Rover Series 3 SWB

Now that would be a result 2006my v8 vogue
Ktm superduke 990