I don't know if your Reznor is an 'open flued' appliance which gets it's combustion air from within the room in which it's installed, or whether it's a 'room sealed' appliance (known in the UK as 'balanced flue') which draws it's combustion air from the flue 'terminal' outside the building, from which the products of combustion ('exhaust fumes') are emitted.
Yellow flames are an indication of incomplete combustion usually caused by insufficient air being drawn into the burner.
Gas appliance burners are basically 'Bunsen' burners, which have a venturi into which 'primary' air is drawn by the stream of gas entering the burner. The air mixes with the gas and 'secondary' air around the flame also aids complete combustion. In an 'open flued' gas appliance burner which draws air from within the room , if any debris such as fluff from clothes, hair from pets, or in your case, dust, enters the burner, the inside of the burner head becomes partially blocked and insufficient air is drawn into the venturi. Thus the air:gas ratio at the burner is insufficiently mixed to enable complete combustion. For this reason, new installations of 'open flued' gas appliances haven't been made or installed in the UK for maybe thirty years, but existing ones are permitted to remain.
Natural gas (methane) is CH4. The carbon atom needs two atoms of oxygen so that when it burns, is creates C02 - Carbon Dioxide, which isn't poisonous. If it only receives one atom of oxygen ('O'), it become CO, which is poisonous. Only a very small amount in the atmosphere is deadly, because when humans inhale air, our bodies much more readily accept carbon monoxide than the oxygen in air. (The hydrogen in the CH4 molecule combines with oxygen to form H2O, which is basically, water vapour). So, in a correctly working gas appliance, the 'fumes' emitted from the burner consist of carbon dioxide and water vapour, which is the same as our breath when we exhale.
The bottom line is: get the burner checked out. A gas engineer who has a flue gas analyser will be able to check in minutes if the problem is indeed incomplete combustion resulting in carbon monoxide, and if so, will not doubt take a close look at the burner.
I hope the chemistry lesson isn't too boring. I spent my 40-year career in the gas industry and in the late 1960s was involved in the design of gas appliance burners to convert gas appliances designed for use on coal gas, to be able to be used on natural gas.
Later in my career (late 1970s'80s), I had to attend fatalities where it was suspected that someone had died from carbon monoxide poisoning, and to attend inquests where that was so. I got to know the Coroner's Officer well enough to receive a Christmas Card from him. A lifetime away, thankfully. As often as not, such sad events were in dilapidated rented properties where landlords failed to have appliances checked and serviced. When one was convicted of manslaughter and jailed, new regulations came into force and all landlords must have gas safety checks carried out and certified annually.
Hope that's of help and interest.
David.
