Have HVAC Questions? Ask an HVAC Expert for Answers
Hello and thanks for using this service, if you have been waiting do not worry or get upset I am just one of the techs on here and I try to get to as many customers as I can and I just picked up your question now. Please give me time to respond as typing, researching and adding links takes me time to do so please be patient and often I will ask you questions to narrow down the issue to get is diagnosed correctly.
There is a good chance the unit is overheating and the thermal rollout is tripping then the blower will just run with no heat until it cools down to reset. Try to change the filter to a less restrictive one or take it out completely and see if it changes the issue at all. If not check the thermal rollout sensor on the burner and change it as it may be possibly defective causing the issue.
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OK read your question....you stated that it will work on heat sometimes and other times the blower runs all the time, you never said it does it from a cold start where did you say that??? I went off your statement!
Take care man
The question is open for other techs to help get you going, we were just not on the same page with this issue. I wish you the best of luck!
Sorry you are having issues. I will be happy to guide you and work with you as a fellow HVAC tech. These furnaces have a diagnostic light as you know.What we have to do is catch the furnace when it is not working and see if we are getting an error code on the board telling us what is failing.I will need to know at what point in sequence it fails and what error code we get at that point.(Examples :If inducer comes on but igniter never lights and blower starts or if inducer works , igniter works, burners come on, then shut right back down and blower comes on, or if nothing comes on period but main blower.)
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Lets start by verifying issue is not in thermostat.When it fails , jump R and W at furnace board and make sure we are telling heat to start.WE will go from there.
I understand the frustration as a fellow tech.If we are intiating heat and sequence does not begin by inducer motor closing pressure switch and beginning ignition we should definitely get an error code. If we are not getting an error code, board has failed to do what is designed for .Possible that you got a DOA board out of the package. Seems unlikely that it would do same as old board. I would make sure unit has a good ground.(Not plugged into a receptacle) and if so my diagnoses would be try another board.