Yes, I have several heated propagators, and there is no way of controlling the heat - they are always on, and seedlings can get fried. When the sun shines into the greenhouse, the temp under the lid goes too high. I want a thermostat to switch on if the temp falls below 21C (70F) which it does at night. By day, the sun supplies all the heat.
A thermostatically controlled propagator is very expensive, and I have seen a few ideas to convert a dimmer switch to a thermostat, keeping most of the components. I want a remote thermistor as the temp sensor. Any ideas?