Yes I have had problems as I leave for work at 7am when it is rather too cool to take the lids off. If they are left on then they get too hot. So I have left the heat on [thermastatically controlled luckily], lid off and so far germination of toms and peppers. Cucs came through in 3 days then got over hot and dropped their seed leaves. Not certain if they will develop any further though.

Thanks. I think they have just burnt up under the thin layer of seed compost on top of them.

I've set 3 types of toms over 3 weeks ago ( garreners delight, sun gold and Marmande) and not one has come up yet. I've no idea what I'm doing wrong - they came up o.k. The last 3 years and I've done nothing different.
But my cucs, courgettes,lettuce,radishes were fine.

Given the temperatures you have been having down south do you really need to use a propagator at all?

No problems at all. I use 1/4 size seed trays placed on an aluminium heat mat that is thermostatically controlled.
The probe goes into a similar sized tray of compost set at 65'c. The trays are covered with freezer bags to form a little tent to keep moisture in.
Tomatoes came through in 5-7 days.
Cabbages and the like are quicker.

I've lost my calabrese seedlings in an unheated greenhouse because I forgot to get their cover off and they got cooked in the recent warm weather, but not a single tomato seedling has appeared yet, and only a single basil one. Getting a tad worried, now.

all my toms are through now, taken 8 days. half the peppers are through now.

Its been down as cold as 6 degrees on a night hence the heat required.

I should be biting my tongue.(or my typing finger) Since I wrote that last comment this morning, 5 tomato seedlings have emerged and decided to prove me wrong. Still only one very sad little purple basil seedling after 18 days, though.