With the fan running all the time I would guess checking C7, C10 and the 555 IC, along with the triac TH2, and D3, C9, Q1, Q2 and Q3. Heater on all the time check TH1 for a short, and if it is fine then the UPC1701 and C2, PUT1 and the wiring to the pots and the pots themselves if they are open circuit.