plugged or stuck thermostat.

 

Don't hurt to try, depends on how bad the chemical or deposit is thats stopping it up. If it does clear it you might find you have a heater core leaking.

It's always better to fix a problem correctly rather than put a band-aid on it. Even if the actual pressure flush works it may reveal a hidden problem and adding chemicals may accelerate problems like rusty freeze plugs.

Guess you'll have to flip a coin.

I had to replace my ac evap. That's a pretty big job having to remove the entire dash, so while I was at it I replaced the heater core, even though I've always kept the coolant flushed annually.

 

Well, I finally got out there and flushed mine. It was NASTY!! The guy before me ran straight water instead of anti-freeze so there was a lot of rust in there. All better now though...now on to the next problem.