No Heat in Millwood, WA

Millwood's housing stock tells part of this story. A lot of homes in this area - including neighborhoods near the Millwood Historic District and along the Argonne Road corridor - were built during building booms 15 to 20 years ago. That means a significant number of furnaces installed with those homes are now at or past the end of their designed service life. Builder-grade equipment installed in 2005–2010 was never meant to run forever, and the components that fail first are predictable.

Here are the most common root causes we find:

1. Failed igniter The hot surface igniter is a ceramic element that glows red-hot to light the burner. It's fragile and has a finite lifespan - typically 7–10 years. When it cracks or burns out, the burner never lights. The blower may still run, pushing cold air through your vents.

2. Dirty or failed flame sensor The flame sensor is a small metal rod that confirms the burner actually lit. When it gets coated with oxidation (which happens naturally over time), it can't "see" the flame and shuts the gas valve off as a safety measure. The furnace tries to light, fails, and locks out after a few attempts.

3. Pressure switch failure The inducer motor creates a draft to pull combustion gases out through the flue. A pressure switch monitors that draft. If the switch fails - or if the inducer itself is weak - the furnace won't allow the burner to fire. This is a safety interlock, not a glitch.

4. Tripped high-limit switch The limit switch shuts the furnace down if it overheats. Overheating is usually caused by restricted airflow - a clogged filter, blocked return, or closed vents. The switch trips, the burner shuts off, and the blower keeps running to cool things down. You feel cold air. The furnace may reset and try again, or it may lock out entirely.

5. Gas valve or control board failure Less common but more serious. The gas valve controls fuel delivery; the control board is the brain of the operation. Either can fail without warning, especially in older systems. These require testing with proper instruments - not visual inspection.

6. Cracked heat exchanger This one matters for safety, not just comfort. The heat exchanger is the metal chamber that separates combustion gases from the air you breathe. When it cracks - which happens as metal expands and contracts over years of heating cycles - the furnace's safety systems may shut it down. Or worse, they may not. This is why a thorough diagnostic includes a heat exchanger inspection, every time.

Before you call, run through these. They won't fix a mechanical failure, but they rule out the simple stuff fast.

• Check your thermostat. Set it to HEAT, set the temperature 5°F above the current room temp, and confirm the fan is set to AUTO (not ON). A thermostat set to ON will blow air continuously - including unheated air between cycles.
• Check the filter. A clogged filter is one of the most common causes of overheating and limit switch trips. If it's gray and matted, replace it before calling. This alone sometimes resolves the issue.
• Check the circuit breaker. Furnaces have a dedicated breaker. If it tripped, reset it once. If it trips again, stop and call - that's a sign of an electrical fault.
• Check the furnace power switch. It looks like a light switch, usually on the wall near the unit or at the top of the basement stairs. Make sure it's in the ON position.
• Check the condensate drain line (high-efficiency furnaces only). These furnaces produce water as a byproduct. If the drain line is clogged, a float switch shuts the furnace down. Look for standing water near the unit.
• Check for error codes. Many furnaces have a small LED that flashes a fault code. Count the flashes and check the code chart on the inside of the furnace door panel.

> If you smell rotten eggs or sulfur at any point, stop. Leave the home immediately, leave the door open, and call your gas utility from outside. Do not operate any switches or flames.