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issue. First I’ll need some more info so I have a more complete picture of you situation
What is the brand and model number of your furnace?
Tell me what happens on start up? where in the ignition sequence does it lock out?
What are you getting for a blink sequence on the control board?
Sounds like a bad connection between the board and the valve. If you didn't replace the wiring harness that would be the next step.
Your voltage reading at the valve is way too low. Should be 24 vac. Since you have a new board there is nothing left except possibly a weak transformer (should put out at least 24 vac) or bad transformer connection. Also looks like there's a fuse in the transformer secondary to the board. Gas pressure is not an issue if you don't have enough voltage to open the gas valve
That's not what I see in the wiring diagram. There is a ground connected to the valve but other than that it connects to a 9 pin connector. Schematic shows a limit control in the circuit before it goes back to the board but calls out only on downflow or horizontal units. You test the transformemr at the transformer. Looks like red & yellow out of the transformer. Pressure switch is not an issue if the igniter initializes.
Yes, ~24 vac
1. Do you have spark igniter or hot surface glow bar
2.Do you get any other error code before the lockout?
The only thing between the gas valve and board is the heat assisted limit. Follow the blue wire and locate that limit.See if we have continuity on limit terminals. See diagram below
Easiest thing to do is just bypass it to se if we get 24v to valve. Disconnect wires from limt and connect them together
You can use a straighten paper clip or anything.I like to use a car fuse.Just anything to connect the female connectors together,If bypassing makes it work switch is bad,
It is just a limit that keeps burners from lighting if blower is not moving enough air across heat exchanger.
They fail just like light bulbs burn out.No set life span. Were you able to bypass and make furnace work?
OK let me know.
Jump the two blue wires together using a fuse or a wire or a straightened paper clip
That is correct.These switches are known to fail and we know furnace is not hot enough to trip as long as blower was coming on.Blower did come on yes?
Tape off the yellow wire and white wire and connect the two blues and let me know if that works.
I see the yellow going to one side of the resistor and white from resistor to the blue.
That is the heat assist part of the switch.Since you are not using a eat assist they should not be needed. Try this, Connect the 2 blues using a fuse or straightened paper clip.Turn power off and back on to furnace and see if it will work or you still get the error.
OK, but it will not work with the 2 blues connected to the new limit and yellow and white taped up?
How about if you leave the yellow ad white connected to the old limit and leave it hanging free, Then connect blues to the new limit.That resistor may have to sense it connected
Yes it is safe.Lets try that next
I am thinking we may have to get it
THat little four wire senses heat somehow from power being applied to valve and the resistance allows it to open or close. I can never tell you to bypass a limit, but if I were cold I might be tempted to run a half hour or so at a time. You do have other limits in furnace to shut furnace down but I can not tell you it is ok.