I have a 15yr plus Olsen furnace forced air, gas. The thermostat doesn't rise over 16 degree's and the fan runs continually no heat but fan runs. For me to get heat I have to crank the thermostat over 30 degree's. Then the fan turn on and about 60 sec later the heat come on. It will reach the 30 degree mark then shut off... and the fan continues to run while the temp drops to a low 16 again... etc I think it maybe the exhaust fan. I'm not sure what's going on here? Any help would be greatly appreciated

Jump the R or RH wire and the W wire on the terminal strip in the furnace. This will eliminate the thermostat control and the furnace should heat all the time. If this works then the thermostat is to blame if notpost back with results.