Put the seeds outside in a shady area and they will germinate. Then put them in sun. No heatpad for lettuce.

I'd use new seeds, not the same ones that were on the heatpad.

Here is a link that might be useful: seed germination temperature chart

Heat pad is most useful for getting heat loving things like tomatoes and peppers up in the cool temperatures of late winter, when your house is still too cold. I don't find I have any use for mine this time of year. I'd also start with fresh lettuce seed at this point too. Cheers!

Just for info. the reason the esacarole germinated is that, although it looks rather like lettuce, it is in a different genus (Cichorium) to lettuce (Lactuca) and has different requirements.

Thanks all!!