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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8265
Experience:  Furnace, A/C and heat pump specialist.
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My burners won't turn on. I replaced gas valve and furnace

Customer Question

My burners won't turn on. I replaced gas valve and furnace control board. It worked for 3 days and now goes into lock out after 3 tries.
Submitted: 9 months ago.
Category: HVAC
Expert:  Rick replied 9 months ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your

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?

Customer: replied 9 months ago.
It is a Rheem..
Customer: replied 9 months ago.
Model number 80pj07ear01
Expert:  Rick replied 9 months ago.

Tell me what happens on start up? where in the ignition sequence does it lock out?

Expert:  Rick replied 9 months ago.

What are you getting for a blink sequence on the control board?

Customer: replied 9 months ago.
At first the burners were not coming on after the igniter would glow. The gas valve was getting 24 volts but not opening. I tapped the gas valve with a wrench and it opened. So I figured bad gas valve and replaced it. Then with the new gas valve on it was not getting 24 Volts from the furnace board so I replaced that as well. It worked for 3 days and now the burners won't kick on after the igniter glows. I am reading o.3 volts at the gas valve as the igniter glows, I hear the gas valve click and my reading shoots up to 1.4 volts at the gas valve for about 5 seconds then drops back to 0.3 and no flames is the result. It tries 3 times then system locks out and I have to reset it
Customer: replied 9 months ago.
After it locks out the light stays on and on the board that is defined as system is in lockout
Expert:  Rick replied 9 months ago.

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.

Customer: replied 9 months ago.
The wiring harness that I used was brand new that came with the board
Customer: replied 9 months ago.
Could low gas pressure be the problem?
Customer: replied 9 months ago.
How many volts am I supposed to read at the gas valve as the igniter is glowing?
Expert:  Rick replied 9 months ago.

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

Customer: replied 9 months ago.
The two lines that connect to the gas valve where I am supposed to get 24volts lead to what looks like a pressure switch that is mounted below the fan and then from that switch back to the board?
Customer: replied 9 months ago.
How do I test that switch and the transformer?
Expert:  Rick replied 9 months ago.

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.

Customer: replied 9 months ago.
I test at the red and yellow wires going into the board from the transformer? What should it read?
Expert:  Rick replied 9 months ago.

Yes, ~24 vac

Customer: replied 9 months ago.
I unplugged the transformer.. called for heat. Taped door switch shut and read 24 volts coming out of transformer
Expert:  airheatman replied 9 months ago.

1. Do you have spark igniter or hot surface glow bar

2.Do you get any other error code before the lockout?

Customer: replied 9 months ago.
Hot surface glow. And no codes it tries how it's it's supposed then locks out
Expert:  airheatman replied 9 months ago.

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

Customer: replied 9 months ago.
How do I test for continuity? What would cause that switch to go bad or trip?
Expert:  airheatman replied 9 months ago.

Easiest thing to do is just bypass it to se if we get 24v to valve. Disconnect wires from limt and connect them together

http://i.imgur.com/WqmGzzO.png

Customer: replied 9 months ago.
What's that piece your using to bypass it? If it works does, what does that mean about the switch?
Expert:  airheatman replied 9 months ago.

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,

http://i.imgur.com/Aqd9O0f.png

Customer: replied 9 months ago.
What does this switch do? Why do they go bad?
Expert:  airheatman replied 9 months ago.

It is just a limit that keeps burners from lighting if blower is not moving enough air across heat exchanger.

Expert:  airheatman replied 9 months ago.

They fail just like light bulbs burn out.No set life span. Were you able to bypass and make furnace work?

Customer: replied 9 months ago.
No I stepped away from the furnace had to pick my daughter. I will try when I get home
Expert:  airheatman replied 9 months ago.

OK let me know.

Customer: replied 9 months ago.
How do I bypass the switch
Expert:  airheatman replied 9 months ago.

Jump the two blue wires together using a fuse or a wire or a straightened paper clip

http://i.imgur.com/Aqd9O0f.png

http://i.imgur.com/WqmGzzO.png

Customer: replied 9 months ago.
I did that and it worked. Does that mean I have to replace the switch?
Expert:  airheatman replied 9 months ago.

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?

Customer: replied 9 months ago.
I went and got a new switch today. The guys said they can't get the original one until Monday and I been without heat for a week with the cold coming in this weekend. They said this could possibly work. How would I go from a 4 terminal to a 2 terminal switch?
Expert:  airheatman replied 9 months ago.

Tape off the yellow wire and white wire and connect the two blues and let me know if that works.

Customer: replied 9 months ago.
I taped off the yellow wires and connected blues to the new switch. It did not work.
Customer: replied 9 months ago.
The yellow wire is a dual wire and goes to the control board and to the gas valve..
Expert:  airheatman replied 9 months ago.

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.

http://i.imgur.com/Aqd9O0f.png

http://i.imgur.com/WqmGzzO.png

Customer: replied 9 months ago.
When i jump the two blue wires with a paperclip it works fires up and blower kicks on.. the two yellow wires from the switch lead to a terminal on the gas valve and the MV COM plug on the furnace board.. one blue wire goes back to the other gas valve terminal (it also has a ground terminal) the other blue wire goes back to the furnace board plug MV HI
Expert:  airheatman replied 9 months ago.

OK, but it will not work with the 2 blues connected to the new limit and yellow and white taped up?

Customer: replied 9 months ago.
No it wont
Customer: replied 9 months ago.
When you say taped up.. is that individually or together?
Expert:  airheatman replied 9 months ago.

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

Customer: replied 9 months ago.
Again should I tape them white and yellow together or individually? If I try leaving them on the old switch and connect the blue wires to the new switch, is that safe for the system?
Expert:  airheatman replied 9 months ago.

Yes it is safe.Lets try that next

Customer: replied 9 months ago.
I just blew the furnace board fuse..I think the paper clipped caused it. I have to go to parts store and buy a fuse real quick
Expert:  airheatman replied 9 months ago.

ok

Customer: replied 9 months ago.
Leaving the yellow and white wire on the old resistor did not not work. It only works when I jump it out? Do I need the exact switch you think?
Expert:  airheatman replied 9 months ago.

I am thinking we may have to get it

Customer: replied 9 months ago.
How does that sensor work technically speaking? What are all the terminals for?
Customer: replied 9 months ago.
Can I safely leave the switch jumped out for the weekend? The earliest I can get the new switch is on Monday. My house was at 68 degrees I called for 70 heat. Burners kicked off and fan ran for an extra 20 30 seconds I'd say after it reached 70. Thermostat ended up reading 71 degrees in the house.
Expert:  airheatman replied 9 months ago.

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.