A compost pile needs temps of over 140F for a week or so to kill weed seeds. Certainly 100F discourages tomato germination. Not clear if that means that the seeds are actually killed, but if a seed is moistened and doesn't germinate, I suspect that changing the temperature won't fix anything.

Same thing happened to me last year. Mine never germinated, so I had to replant. This year I kept them on the heat mat till they sprouted, then moved them to the grow light.

Personally I'd replant and not count on much if any germination from them. Is your heat mat thermostatically controlled? If not it should be. If so then there is something wrong with the thermostat.

Dave

It’s funny you say that. I dug around a bit, and a fair percentage of the seeds are sending out a radicle after three days. I may stick a couple extra seeds in there just for insurance, and I did get a thermostat for the heat mat. It’s around 77-81 now.

I got away without one before, but it was a cheapo 18 watt, this one is much more powerful.

Actually about 70% coming up now.

I geminate peppers in 100F, they love it. I wouldn't be worried about your tomatoes.

That's interesting about germinating peppers at 100F. Extension services say that 95F is the "maximum" for pepper and tomato germination (as opposed to "optimum", which is 85F), but I've always been suspicious of those numbers.

It is not a consistent lt 100F, but they can hit it over my radiator as the heat is running and come up in 7-8 days.

My tomato seeds always seem so much less picky than the pepper seeds. Glad to hear they are coming up!