will seeds get overheated in a heated propagator within a greenhouse?
I am having mixed results
Would have thought so Del but I suppose it depends what you're growing. Are you making sure they get ventilation too?
I've got heated propagators in my greenhouse, not the fancy ones with thermostatic controls, and find them invaluable for starting stuff off early. But yes, seeds and seedlings can get overheated if it's sunny as well, as I found to my cost when I came back to find my first sowings of courgettes and cucumbers had effectively been cooked in there.
I'm sure they would have been fine if I'd either removed the lid, or turned the unit off.
I run my propagator in the shed out of the sun to avoid cooking the seeds. I take them out of the propagator as soon as they germinate and into the cold greenhouse. I don't use it often though. Seeds seem to germinate without.