said by Worried :
I have already replaced the t'stat but nothing has changed. Please advice to what may be the cause so that I can have a professional fix it. Thanks a lot !
You need a professional if you didn't figure out if the thermostat is broken before replacing it.
A thermostat is a dry contact switch. There will be 2 LV DC wires coming from "the house" (thermostat+random safety sensors) to the burner control. If there are more wires, then ignore this advice. The wires to the house should measure less than 1 ohm/0.0 if there is a call for heat. If you shore with alligator clips the 2 terminals in the burner control, you will be pretending to be a thermostat and turn the burner on.
As already said in this thread, if you have to power cycle it, a safety sensor went off somewhere and that is beyond your skill set to fix. Worst case scenario if you fix it yourself, explosion/house fire or carbon monoxide death.