I can turn on the heater at the thermostat and the fan blower comes on. Periodically the electric glow rod (?) lights up but it does not light any gas in the three tubes (burners). I do not smell gas. There is gas going into the house as the gas fireplace and water heater works and I have verified that the manual gas valve is turned on to the central heater. However, no gas is getting to the burners or three tubes in the furnace. Approximately 4 years ago, the Honeywell SV9501 control valve was replaced. Please help! :(