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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22009
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Have a York Diamond 80 that is showing an error code of 4 blinks

Customer Question

Have a York Diamond 80 that is showing an error code of 4 blinks - open limit. Where is the high limit switch?
Submitted: 5 years ago.
Category: HVAC
Expert:  BillyHvac replied 5 years ago.


The limit is commonly a flat plate above the burners and has 2 wires attached. It doesbt look like much because the switch is acually inside the furnace. Many times you clean and tap it and it will reset. If not it will need to be replaced.



Customer: replied 5 years ago.
Would it have a clear "vacuum" tube attached to it? We're expecting 18-24 inches of snow and am dreading a service call. I read that the switch could be tripped if there was a power failure while the furnace was running hot, also how do I determine up vs down draft? The furnace is an independant zone for the 2nd floor and is located in the attic. Thanks for your help.
Expert:  BillyHvac replied 5 years ago.


The limit switch is a high temp switch in case of high temps in furnace from blocked filter, blocked register, bad blower. The pressure switch ( with the tubes) would not make contact if the outside sections of pipe were to get covered up.


Updraft means the furnace blows air straight from a basement....down draft and horizontal are commonly found in attics

Customer: replied 5 years ago.
Ok, so we now know that it is a downdrafting York Diamond 80 (propane). It appears that the unit itself is mounted horizontally. I can see a row of burners (5 i think) that are mounted vertically roughly 2" from the flashing LED. I haven't yet found the limit switch, I'm gonna take some photos...
Expert:  BillyHvac replied 5 years ago.


Photos will help greatly



Customer: replied 5 years ago.
Letting unit reset. Found what I think is the switch. Texas Instruments piece with 2 wires going into it with 2 bolts attached. When removed from burner has about 3-4" "arm" that sticks into burner. Looks clean, gave it a few taps. I'll let you know.
Expert:  BillyHvac replied 5 years ago.
Keep me posted

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