temperature controlled heat mat success

The heat mat I fixed three days ago has delivered We’ve had lettuce seeds in a cold frame from two weeks to no joy so far, whereas a new batch with heat @ 20°C looks like a win in three days.

lettuce seedlings germinated in three days @ 20C

Now I just need to get a control on the Sankey propagator which uses four times as much power for an area about one-sixth of the size. For all that power it does raise the temperature to over 30°C which is unnecessary, and possibly slightly detrimental.