Odd heater question

Ok so my 1997 xk8 has had an issue since i bought it. When i turn on my heat, it starts getting warm air within a half mile from the house, then it gets nice and toasty for about 10-15 minutes. Then all of a sudden like, it seems like the heat drops down and doesn’t usually pick back up again. Ive searched the archives, but usually people have no heat at all. Just thought I’d put it out there for ideas

Are you using the climate control setting?

Is the electric recirculation pump whirring? It’s a bit awkward to get to on rh side as you face engine it’s tucked behind the coolant filler tank on the firewall. You can probably check by putting a long screwdriver on it and put your ear against it to see if you can hear the motor running. It’s a bit of a mare to change though.

I just set the temp to 72 and usually defog. I dont use the auto button at all if thats what you mean

Ill have to check. Should it be whirring constantly, or just sometimes. Should I check only when it stops heating?

So it was suggested for me to try unplugging my heater valve and WOW what a difference! I did my first drive today and needless to say it stays VERY toasty! Ill look into a couple of other things when it warms up outside a little more lol!