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Burners are lit with an electronic ignition , no pilot. Does unit work in Cool mode and can you do some hands on troubleshooting?
Give it a few minutes until thermostat COOL turns solid and stops flashing.It is in a delay.
OK do this so we can make sure issue is not with thermostat.
On control board in unit, jump the R and W terminals and see if heat will come on.
That is correct where red and white connect to board.What we are doing is bypassing thermostat to eliminate it being the issue.
OK disconnect all the thermostat wires from the board outside and then jump R and W as shown earlier and see if heat will come on.
Can you send me a picture of what you are referring to?
If you have a paper clip icon on your page you can attach using that link.Or
You can upload the pictures using the tiny pic site .
Here is a link to the site.
Click on Browse , select the file from your folder.then click UPLOAD NOW.
They will give you a quote to enter in the box to verify you are a human.Enter the quote and click UPLOAD NOW
You will see your picture on right side of screen.
Then copy the link URL for email & IM
Paste that link here on the site.
OK let it try several times in case there is air in the gas line.You may have to power it off and on if it goes into lockout.
Is the error light flashing o board? If so how many flashes between pausing?
Look near burners for a flame rollout that will reset by pushing button in center
Youmay have 2 or 3.see if any will click and reset then try heat again
Remove wires and connect them together using a paperclip or small nail to see if this is the issue.
Ok now you have at least one more limit that can do this,but it is not resettable and one in furnace chamber.You can ohm them with wires unplugged or bypass for a test.
The board as you see has a 12 pin connector. Wire leaves pin 3 and goes to aux limit on blower housing, then to rollout switch and then to gas valve. If rollout or aux limit is open, we get no signal to valve.
Wire leaves pin 4 and goes to main limit then back to pin 1.If limit is open board senses and will not allow heat to come on.
You can verify limits are "closed" and if so, push in on the wires at 12 pin plug to make sure they are making connection.Also wiggle or unplug and re plug 9 in just so we know it is making good connection.
OK You are correct.the numbers are a bit hard to see on my diagram. 4 and 5 are indeed the main limit circuit.It must be closed.
Make sure wires are seated good and plug and unplug the connector if circuits are closed.
OK these wires are 24 volt wires, You will have a 24v common going to valve at all times from blue at contactor. On call for heat, the 24v HOT is sent from board, through aux limit then to and through flame rollout to gas valve to close the 24v circuit and energize valve
Excellent. This is not the issue then
Lets chek between 4 and 5 to make sure main limit is good and is closed.
I am beginning to suspect we may have a failing board.Try heating the board with a hair dryer to just above warm to touch and see if we get any different reaction.Sometimes they get stress cracks and sometimes actaull short internally.The blown fuse is also common if board is shorting.
Not that bad, About a hundred bucks.