<< Last spring someone mentioned they used a used water bed heater for starting seeds. Where did you put the probe aka temp sensor? >> I don't remember if I made the original post, but I also use an old water bed heater. I use a seed starter kit with a plastic tray, cell packs for planting the seeds and a clear cover. I just put the probe at the bottom of the tray between the cell pack cells in the center and put on the cover as best as I can with the probe wire running under it. If you're using individual pots or cell packs, try putting it under whatever container you use. You may need to use something else as a spacer under the container to keep it level. You also might check to make sure the temperature setting on the heater is reasonably accurate. Regards, Rick