PCs don't usually use that much power however heaters can, might be worth looking at how many amps your circuit is versus amps chewed up by your heater.
Your fuse box will hopefully have written on each fuse the amount of amps per fuse, usually 15, 20, or 30. One of those fuses will be connected to circuit in the room in question and hopefully labelled.
Meanwhile for the heater, figure out how many watts it uses then convert to amps. For instance at its highest setting, my heater is 2400 watts. Plugged into a 240 volt PowerPoint it uses up 10 amps
This shouldn’t be the case, report it as it might be a potential electrical fault. (Assuming the 2 items are not triggering on their own, in which case don’t use the triggering one again, it is unsafe)
Yeah the PC is all good on its own, and I'm going to give the heater a go on its own tomorrow when nobody's home (there's 4 rooms all on one circuit (I think?) And we all have our heaters going, so I suspect that's probably the issue)