My propagators are in a frst free greenhouse - heater cuts in to keep a minimum 5 deg C.
This non-thermostat propagator only had 8 seeds sown in it (which you can see at the bottom of the pic) before I went away for a week, deciding to leave the rest of sowing until a bit later. This pic is taken three weeks later. I think the propagator normally heats quite evenly, but it was persistently cold and you can see from the pattern of the dried out cells the impact of the cold air around it (it has a plastic lid by the way). I'm surprised so many of the 8 germinated.