Error Code Limit Switch Open

York TM9V080B12MP11 Error Code Limit Switch Open: Limit Switch Open

TL;DR
Your York furnace has tripped its high limit switch or blown the 24V fuse due to overheating. The most common fix is replacing a clogged air filter and making sure all vents in your house are open.
Disclaimer
This article is for informational purposes only and does not guarantee the accuracy or completeness of the information provided. Always turn off power and gas supply before attempting any repairs. If you smell gas, leave immediately and call your gas company. Consult a licensed HVAC technician for diagnosis and repair. Any actions taken based on this information are at your own risk.

What Does Code Limit Switch Open Mean?

The 4-red-flash code on the York S1-33103010000 control board indicates that either the high-limit switch has opened due to overheating or the 24-volt fuse on the control board has blown. In most residential situations, the overheating scenario is far more common than a blown fuse.

The high limit switch is a safety device that monitors the temperature of the air leaving the heat exchanger. When the blower cannot move enough air to carry away the heat being produced by the burners, temperatures inside the furnace rise until the limit switch opens and shuts the burners down. The furnace will not restart until it cools sufficiently for the limit switch to reset.

A clogged air filter is the most frequent cause — it is also the easiest to fix. Blocked supply or return registers throughout your house create the same problem by restricting the total volume of air the blower can circulate. If the filter and vents check out, a blown 24V fuse on the board or a failing blower motor may be the culprit, which requires professional service.

How to Fix It: Check and Replace the Air Filter + Open All Vents

âš  Safety First
Always turn off the furnace at the power switch or breaker and shut off the gas supply before beginning. Do not proceed if you smell gas — leave the area and call your gas company immediately.

What You'll Need

Steps

  1. Turn off power AND shut off gas supply Turn the furnace power switch OFF. Turn the gas shutoff valve to OFF (perpendicular to the pipe). Wait 5 minutes. If you smell gas at any point, leave the area immediately and call your gas company.
  2. Locate and inspect the air filter On York furnaces, the filter is usually in the blower compartment behind the lower access panel or in an external filter rack. Slide it out and check the size printed on the frame. Hold it up to light — if it is opaque with dust, it needs replacing.
  3. Install a new filter Insert the new filter with the airflow direction arrow pointing toward the blower (toward the furnace). Make sure the filter sits securely in its track.
  4. Open all supply and return vents Walk through every room in the house. Ensure all supply registers and return air grilles are fully open and not blocked by furniture, curtains, or rugs. Even closing a few registers in 'unused' rooms can cause airflow problems.
  5. Restore and test Replace access panels. Turn gas ON (parallel to pipe). Restore furnace power. Allow 5-10 minutes for the furnace to cool and the limit switch to reset. Then set the thermostat to call for heat.
How to Verify
After the furnace restarts, the LED should show a slow amber flash (call for heat in progress) transitioning to slow green (standby) when the thermostat is satisfied. If 4 red flashes return, the problem may be a blown 24V fuse on the board, a failing blower motor, or a defective limit switch — all of which need professional diagnosis.

When to Call a Professional

Contact a licensed HVAC technician if:

Sources

  1. Johnson Controls S1-33103010000 Installation Manual (ManualsLib)
  2. GHAC Knowledgebase
  3. Gray Furnaceman (grayfurnaceman.com)
  4. Advanpro Calgary