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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8369
Experience:  Furnace, A/C and heat pump specialist.
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My furnace is showing an error code of secondary voltage

Customer Question

My furnace is showing an error code of secondary voltage fuse short. where do I locate this?
JA: How old is the appliance? Have you gotten error messages before?
Customer: 18 yrs. 58PAV upflow. I have repaired?changed my flame sensor, ignitor, and limit sensor previously as well as a professional replaced the blower.
JA: Do you plan on doing the work yourself?
Customer: This started after having a gas line installed for a gas range. Initially this started with the flame roll out/limit switch being tripped. We got it going then it stopped again and we now have a #24 error code.
JA: Anything else we should know to help you best?
Customer: If possible, I have done it many times before with a walk through from an HVAC technician Thank you
Submitted: 9 months ago.
Category: HVAC
Expert:  airheatman replied 9 months ago.

My name is ***** ***** I am happy to assist you today.Give me a moment to look over your question and gather some information .I may need to get a bit more information from you.

Expert:  airheatman replied 9 months ago.

Secondary use will be on control board in blower compartment.See links below.Remove the fuse and see if it is blown.

Customer: replied 9 months ago.
yup- and of course I have fuses from 5-30 in my garage but no 3!
Customer: replied 9 months ago.
can I at least test it with a 5? Just to cut down on number of trips to the hardware store.
Expert:  airheatman replied 9 months ago.

Absolutely.If it pops again you have a short and that will requires some troubleshooting.

Customer: replied 9 months ago.
What could have caused the fuse to blow?We were troubleshooting it and it had come on but we did have to restart the process a number of times
Customer: replied 9 months ago.
the blower started but no ignition. error code 21
Since I had a gas line put in for a stove, could he have done something that has caused this problem? (since it's gas valve relay or short to gas valve wire) He's a friend who is a plumber so I don't want to be too accusatory
Expert:  airheatman replied 9 months ago.

The 21 error is stuck gas valve relay or miswire.

Check to see if you are getting 24v to valve with furnace off?

Customer: replied 9 months ago.
On my chart it is #21
I will check the voltage
Expert:  airheatman replied 9 months ago.

Yes I saw and changed my response (typo)

Customer: replied 9 months ago.
I have voltage
Expert:  airheatman replied 9 months ago.

You have voltage to gas valve with thermostat OFF?

Customer: replied 9 months ago.
oops, missed that part, will recheck
How much voltage am I supposed to have? Any? because the needle is moving to between 50-100?
Everything was shut off. thermostat, switch and reset switch all off
Expert:  airheatman replied 9 months ago.

With thermostat OFF we should get 0 voltage at gas valve.On al for heat when burners should light we should get 24vac

Customer: replied 9 months ago.
was I supposed to be checking with my probes to where the fuse was? because that's what I was doing
Expert:  airheatman replied 9 months ago.

At gas valve

Customer: replied 9 months ago.
ok, I have to learn how to do this. you tube, here I come
Expert:  airheatman replied 9 months ago.

The error is saying the gas valve is getting 24vac when it should not or the relay built into valve is stuck

Customer: replied 9 months ago.
I checked at the gas valve itself and there is no voltage.
Expert:  airheatman replied 9 months ago.

OK but still have the 21 error?

Customer: replied 9 months ago.
Again, I had a gas line put in, could there be a switch that was not turned back on fully where my furnace is not getting enough gas?
Expert:  airheatman replied 9 months ago.

You could possibly not be getting sufficient pressure to valve, Can you check or have him check inlet pressure at the valve?

Customer: replied 9 months ago.
sounds like I really do need an HVAC person here. I do not have the knowledge or the equipment to check that. #@%*!
I was really hoping to solve this myself as I have other times.
Expert:  airheatman replied 9 months ago.

I understand.It appears you have gone as far as you can without the tester to check pressure. Next step is to get the pressure checked or replace valve and see if that solves.I just hate being a parts changer.

If you have further questions, please let me know.

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