Furnace will not start on its own. If I tap the relay, or side of the furnace it will fire up and stay running till the thermostate shuts it off. But will not fire up on its own. We had a furnace man come out and he said the relay was toast and probably took the modual out. Told us to buy a new furnace, charged my daughter 160.00 and left. If I tape on the side of the furnace it will fire up. I have looked everything over, leads wires etc, and figure its just something easy but am stuck at tapping the furnace and it will fire up and work just fine. I hold my hand on the gas valve, tap the furnace and can feel the gas valve open and it fires up. Not sure what I need to do.