Ruud UGPH-07EAMGR Error Code 3 Blinks (2-sec pause): Limit Switch Is Open

What Does Code 3 Blinks (2-sec pause) Mean?

A 3-blink pattern on the Ruud UGPH-07EAMGR status LED indicates that the limit switch is open. The high-temperature limit switch has tripped because the furnace is overheating, and it has shut down the burners as a safety precaution. The blower will continue running to cool the heat exchanger.

The most common cause is a dirty or clogged air filter. When the filter is loaded with dust and debris, it restricts airflow across the heat exchanger. With less air to absorb the heat, the exchanger temperature rises until the limit switch trips. Blocked or closed supply and return vents throughout the home have the same effect — they reduce total system airflow.

Other possible causes include a failing blower motor that is not moving enough air, a faulty limit switch, or a wiring issue. The manual advises checking that the limits are closed and checking the wiring. If the filter is clean and vents are open but the limit keeps tripping, a professional needs to diagnose the root cause.

Common Causes

How to Fix It: Replace the Air Filter and Restore Airflow

What You'll Need

• Replacement air filter (correct size for your system) 🛒 Find at FiltersFast · 🛒 Find at Amazon
• Flashlight

Steps

1. Turn off electrical power at the breaker and shut off the gas supply valve Locate the furnace circuit breaker and flip it to OFF. Turn the gas shutoff valve to the OFF position (handle perpendicular to the pipe). If you smell gas, leave immediately and call your gas company.
2. Check and replace the air filter Remove the air filter from the return air duct or furnace filter slot. If it is visibly dirty or clogged, replace it with a new filter of the correct size. Make sure the airflow direction arrow on the new filter points toward the furnace blower.
3. Open all supply and return vents Walk through every room in your home and ensure all supply registers and return grilles are fully open and not blocked by furniture, curtains, rugs, or other objects. Even a few closed vents can reduce airflow enough to trigger the limit switch.
4. Inspect the blower compartment With power off, look through the access panel at the blower wheel. If it is heavily coated with dust, this reduces its ability to move air. Also verify the blower wheel is securely attached and not wobbling on the motor shaft.
5. Restore power and gas, then test Turn the gas supply valve to ON (handle parallel to the pipe) and flip the circuit breaker to ON. Set your thermostat to call for heat and monitor the furnace through a complete heating cycle. Watch the status LED for the 3-blink pattern.

When to Call a Professional

Contact a licensed HVAC technician if:

• The 3-blink code returns after replacing the filter and opening all vents
• The blower motor is not running or sounds abnormal
• The furnace overheats within the first few minutes of operation
• You hear clicking sounds from the limit switch repeatedly tripping
• The blower wheel is heavily clogged with dust and cannot be cleaned easily

✓ Verified against manufacturer service manual — March 2026