A lot of older units will not have a proper ground wire to them. The ground wire I am talking about will be coming in with the high voltage (110 and 110 equaling 220) electrical wires to the unit from the electrical service panel. Some people try and ground unit's through the duct work or metal hanging strap and it fails. The theory behind that is metal anything will make a path to the home (which is grounded) and in these cases you will not have a ground wire to the unit. Not the sure fire way to ground anything and not to code and many, many false ground readings effecting flame sensors because of this. The flame sensor has to have a solid ground to sense the flame or else it will not always ignite as it's only sometimes sensing the flame. If it does not always sense the flame it acts like it has a mind of it's own, seriously tempermental, sometimes on and sometimes off, like you are experiencing.
You need a solidly connecting ground wire from the home's electrical service panel to the unit.
No two ways about it. Have that done and your flame sensing problems are over.
The Following User Says Thank You to Doc Holliday For This Useful Post:
Thanks again guys for the safety tips. I may be doing a lot of renovation on my kids homes in the near future so those common sense reminders are good to know.
I haven't changed any of the wiring other than installing the igniter. I'm pretty careful when it comes to gas and electricity. I just cleaned all the connections on the terminal block and checked connections.
This morning the heater came on after only 30 minutes and it's raining and cold outside. I believe, if the unit keeps working the way it is, I can direct my efforts to other issues. If it goes bad again I'll just buy another flame sensor and hope that does it.
We are budgeting for another unit for next season.
I really appreciate the input from the professionals and others who have contributed.
Thank you again.
P.S. I'll be starting a new string about the furnace under my daughter's 1925 era house which is sitting in a five foot deep dirt hole. I need to disconnect it and pull it out.