Depends what it’s been stuck on with, how much ‘gunge’ used and how well it’s been stuck on If architrave meets plaster wall, cut down joint with a flexi blade craft knife to separate otherwise you run the risk of pulling plaster of with timber Then use a wide blade chisel and hammer / mallet / and get under architrave by 25mm or so and then start to prise off. Start at one end and work along the length, likely that once you start to separate the architrave from door frame, it gets easier as you can then lever the architrave and continue with the chisel If you don’t have a wide chisel, a stiff wallpaper scraper may do but the £ shop cheap jobbies won’t survive being hit with a hammer Probably some type of No Nails adhesive used and this will also need to be removed before fitting new architrave Blobs of No Nails will remain on one surface or the other, so if remains on door frame, again chisel to remove Shouldn’t be too much of a problem ?
If you are trying to limit the damage to surrounding areas tap a thin bladed scraper through the front joint line, pride it apart gently then run a handsaw blade up and down the architrave length gently. Multitool is probably the easiest way short of ripping it off with damage.
Sounds like your replacing architrave anyway so no problem with wrecking it I guess ? As I said, just depends what they’ve used and how much - in your case, it’s well stuck Using a wider blade/scraper will help but needs to be sturdy and not flex too much Would be neater/quicker if it popped off in reasonable sized lengths but if it resists and comes away in fragments - then so be it Clean up frame and remove blobs of adhesive and old architrave before fitting new One way or another it will come off
Used the scraper method and the smooth blade you get with the multi tool, in fact it is the only thing I have used the smooth multi tool for. Both were successful. Does make me wonder what is the best product to use for sticking skirting and facings on with, silicone, stixall, low expansion foam, none of the above and just mechanical fixings? I usually use whatever is in my silicone gun except if it is caulk and back up with the occasional 18g pin. But what is best as a compromise between security of fixing and future ease of removal?