Earlier, the gas would not kicked in. Service tech cleaned igniter, replaced ignition kit (computer board). It worked for 1 month. Now furnace turns on and off frequently without reaching to set temp (70c). I also changed thermostate and still the problem remains!
The furnace is Intercity product RPJII, model # GNJ075N12A1, 15 year old.
Is there any solution OR I need to replace the furnace? Please help.

Call your dealer back there should be a warranty on the work they did it sounds related is the thermostat digital or mercury