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When my natural gas furnace lights it makes a loud bang? What would cause this?
What you are experiencing is a delayed ignition of the burner gases. What happens is dust and spiders build nests in the burners and the orifices and the gas instead of coming out the burners straight to the ignition source like it should, it gets out of wack from the dust and or spider webs and nests and it will not ignite till there is a build up to the ignition source. What I would do is pull the burner and clean them with a wire brush then shop vac the burners. Clean the heat exchanger by running the shop vac into the heat exchanger and using a very small allen wrench or tooth pick, clean the small holes of the burner orifice with the allen key and then use the shop vac to suck out each orifice. Put the furnace back together and turn the thermostat up to see if the furnace ignites right away.
Great, if this doesn't work is there anything else I should try?
You could try re-positioning the pilot assembly for better ignition on start up.