Please help. I am at a loss I have a 14 y/old coleman furnace in my home that has started acting up latley. It is model # BGU07516. The furnace will occationaly work. Whne the thermostat calls for heat the sequence works and the burner will light and the furnace starts to blow hot air. Everynow and then it would call for heat and the vent motor would come on but the burner wouldn't light. I thought the ignition control module was bad so I replaced it the original robertshaw with a white rogers that has diagnostic lights on it. After I installed the new module the furnace worked OK for a day but then I came home from work and the house was 50 degrees I check ed the furnace and the vent motor was running but no heat. The control module was giving me a code for weak flame. I reset the furnace and it seemed to work fine for a couple of hours and then the same thing happened. I am imagining the HSI is going bad but it glows very bright. I would replace it as I don't think they are that expensive but I can't figure out how to get to it on this furnace. Any ideas if this is the problem and if so how do I tell what model HSI to buy and how do I get to it to change it.

Thanks

One thing as a homeowner you can do is clean the flame sensor. For some reason this little part causes many problems with modern day furnaces. Stay away from the item called the ignitor when you are cleaning the flame sensor since they are very easily broken. Also never touch the ignitor in the black areas since that can damage it. Sometimes the ignitor is in a close relationship with the sensor. Below is a few pictures of sensors. Clean with steel wool, scotch brite pad or sand paper.

I believe that the igniter on this unit acts after the burner lights as the flame sensor. Please correct me if I am wrong.

Does your ignitor look like this?

Not sure. I haven't figured out how to get to it yet. The only access I can find is going to require me to open and remove the gas line/valve and I am not sure I want go through that yet.