This circuit is intended to control a heating system or central heating plan, keeping constant indoor temperature in spite of wide range changes in the outdoor one. Two sensors are needed: one placed outdoors, in order to sense the external temperature; the other placed on the water-pipe returning from heating system circuit, short before its input to the boiler. The Relay contact wiring must be connected to the boiler`s start-stop control input.Controlled by indoor and outdoor temperature
Simple, high reliability design.
This circuit, though simple, has proven very reliable: in fact it was installed over 20 years ago at my parents` home. I know, it is a bit old: but it is still doing its job very well and without problems of any kind. When Q1 Base to ground voltage i