Temp gauge all over the place; overheating?

[Algol]

Weird symptoms today.

1. I put the heater on and it took ages to give out heat, despite clearly being warm enough according to the temp gauge.
2. Then, pretty much simultaneously, the heater started to work and the temp gauge needle started going waaaaay up, then back down to normal (just below halfway)

[tashtego]

Maybe a blocked up heater matrix?
Cheers

[POPEYE]

The heaters and cooling systems on these trucks seem to have a mind of their own, I've had my surf for over 12 years and in all that time I have NEVER EVER had nice hot air out of my heater, this is despite me becoming "anal" about my coolant, scared about the rep these things had regarding