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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 7718
Experience:  Furnace, A/C and heat pump specialist.
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Do you know what a fault code 56 means on a thud/theme

Customer Question

Hi do you know what a fault code 56 means on a thud/theme furnace model # r92p0851521msa
JA: Did you check the furnace's filters?
Customer: Yes they are new
JA: Do you plan on doing the work yourself?
Customer: Yes
JA: Anything else we should know to help you best?
Customer: Unit powers in. Then goes through three cycles in heat mode. I checked the igniter and the flame sensor both are ok.
Submitted: 1 month ago.
Category: HVAC
Expert:  airheatman replied 1 month ago.

This a pressure switch error I believe.Are you sure it is 56 not 55?

Customer: replied 1 month ago.
Fault code is 56.
Expert:  airheatman replied 1 month ago.

My manual jumps from 55 to 57

Expert:  airheatman replied 1 month ago.

Chart

Customer: replied 1 month ago.
Only way I believe it could be 55 if the led is bad. Anyway to know which pressure switch they talking about.?
Customer: replied 1 month ago.
Are the pressure switches related to the exterior vents?
Expert:  airheatman replied 1 month ago.

The vent inducer comes on and pulls a vacuum through the rubber hose to close the switch.Is the inducer fan running?

Customer: replied 1 month ago.
inducer fan is running
Expert:  airheatman replied 1 month ago.

OK take the little rubber hoses loos, blow through them and make sure there is condensation or debris in hten.Cleab fittings on switch and inducer housing using a straightened paper clip.Also make sure drain is not stooped up or any standing water in drain

Expert:  airheatman replied 1 month ago.

Pressure switch

Customer: replied 1 month ago.
Removed all hoses and blew them. All clean and clear. Removed the pressure switch. Cleaned as suggested. Checked the drain and hose all clear. Different result now. Now runs a bit longer between cycles. Before 15 seconds between cycles. Now about a minute. Waiting for code it's on its second cycle now.
Expert:  airheatman replied 1 month ago.

Let me know code

Customer: replied 1 month ago.
Just started Third cycle.
Expert:  airheatman replied 1 month ago.

Standing by

Customer: replied 1 month ago.
Thanks.
Customer: replied 1 month ago.
Only good part. Is I have another unit I am not using in the house so if I need and pressure switch I could rob that one to make this one work.
Customer: replied 1 month ago.
Same code. Flashes 1 0 5 6
Expert:  airheatman replied 1 month ago.

You want to try swapping switch?

Customer: replied 1 month ago.
K. Give me a couple minutes.
Expert:  airheatman replied 1 month ago.

Take your time

Customer: replied 1 month ago.
Swapped. Waiting for unit to do its thing.
Expert:  airheatman replied 1 month ago.

Standing by

Customer: replied 1 month ago.
Starting. Inducer running.
Customer: replied 1 month ago.
Flame on.
Customer: replied 1 month ago.
Blower on.
Customer: replied 1 month ago.
Keeping fingers crossed.
Expert:  airheatman replied 1 month ago.

I will stand by.Watch it a few minutes,If it stays running we know we just have a bad switch

Customer: replied 1 month ago.
Damn. Just started second cycle
Customer: replied 1 month ago.
What does this pressure monitor? Exhaust? Or the intake pressure?
Expert:  airheatman replied 1 month ago.

OK we have something either blocking drain , blocking intake or exhauset or losing vacuum somewhere. Have you checked vens outside? I have see as small as a spider web cause loss of enough vacuum to keep switch closed

Expert:  airheatman replied 1 month ago.

The inducer draws in fresh air from outdoors, It proves that vent is not blocked and drain is free and clear. If we get an obstruction anywhere, it allows switch to open

Customer: replied 1 month ago.
If I jump the switch should the unit run if it is that issue.
Expert:  airheatman replied 1 month ago.

Switch has to be open in beginning of cycle.Then you can jump once inducer starts

Customer: replied 1 month ago.
Ok last question if you can. I jump it out and get the same result. The installer has 2" pipes on this unit would larger pipes be better.
Expert:  airheatman replied 1 month ago.

No the 2 " pipes are normal.May be an issue with the board not recognizing it closed if you want to try swapping boards

Customer: replied 1 month ago.
I am guessing the exhaust is the problem because the unit does the same thing with the furnace cover off. So it is getting more than enough air on the inbound side.
Expert:  airheatman replied 1 month ago.

I would try swapping boards

Customer: replied 1 month ago.
K I will that a try.
Customer: replied 1 month ago.
Board swapped.
Customer: replied 1 month ago.
First cycle started.
Expert:  airheatman replied 1 month ago.

Let me know

Expert:  airheatman replied 1 month ago.

Did board make a difference?

Customer: replied 1 month ago.
What a night up till 2am trying to figure this issue. The installer never put in the drain plug on the drain trap. Took it off the other unit and now running. Thanks for your help.
Expert:  airheatman replied 1 month ago.

WOW. Glad you got it working.

If you have further questions, please let me know.

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