No Heat in Nine Mile Falls, WA

Nine Mile Falls has seen steady residential growth over the past two decades. A lot of that housing stock homes built 12 to 18 years ago came with builder-grade furnaces. Many of those systems are now hitting the end of their designed service life. That's a pattern we see every winter.

Here are the most common root causes behind a furnace that won't heat:

1. Failed Igniter (Hot Surface or Spark) The igniter is what lights the gas burner. Hot surface igniters are ceramic and brittle. They crack from age and thermal stress. When the igniter fails, the gas valve opens but nothing lights. The furnace detects an unlit burner and shuts down as a safety measure. You get cold air or no airflow at all.

2. Flame Sensor Failure or Contamination The flame sensor is a small rod that confirms the burner actually lit. Over time, it develops an oxide coating. That coating prevents it from reading the flame correctly. The furnace lights, runs for 2–3 seconds, then shuts off. This is called "short cycling on flame-out." It's one of the most common no-heat calls we run in this area.

3. Pressure Switch or Draft Inducer Problem Before the burner lights, the furnace runs an inducer motor to clear combustion gases from the heat exchanger. A pressure switch confirms that airflow is happening. If the inducer motor is weak or the pressure switch has failed, the furnace locks out before it ever tries to light. You get a blower that runs but no heat.

4. Tripped High-Limit Switch The high-limit switch is a thermal safety device. If the furnace overheats usually from restricted airflow it trips and shuts down the burner. A dirty filter is the most common cause. The furnace may restart after cooling down, but it will keep tripping until the airflow problem is fixed.

5. Gas Valve or Gas Supply Issue If gas isn't reaching the burner, nothing lights. This can be a failed gas valve, a tripped manual shutoff, or a supply pressure problem. Gas valve failures are less common than igniter or sensor failures. But they do happen especially on older systems.

6. Control Board Failure The control board is the brain of the furnace. It sequences every step: inducer on, pressure switch confirmed, igniter warm, gas valve open, flame confirmed, blower on. A failed board can interrupt any step in that chain. Boards fail from age, power surges, and moisture.

7. Cracked Heat Exchanger This is the most serious finding. The heat exchanger is the metal chamber that separates combustion gases from your breathing air. A crack allows carbon monoxide to enter the airstream. A furnace with a confirmed cracked heat exchanger should not be operated. We check for this on every diagnostic visit.

Before you call, run through these. Some no-heat calls have a simple fix you can handle yourself.

• Check the thermostat. Make sure it's set to HEAT, not COOL or FAN. Set the temperature at least 5°F above the current room temp. Replace the batteries if it's been more than a year.
• Check the filter. A clogged filter is the single most common cause of furnace overheating and shutdown. If it's gray and packed with dust, replace it before you do anything else.
• Check the circuit breaker. Furnaces run on electricity even if they burn gas. Find the furnace breaker in your panel. If it's tripped, reset it once. If it trips again, stop and call.
• Check the power switch. There's usually a wall switch near the furnace that looks like a light switch. Make sure it's on.
• Check the furnace door panel. Most furnaces have a safety interlock that cuts power if the access panel is loose or off. Press it firmly closed.
• Check the condensate drain (high-efficiency furnaces). If your furnace has a white PVC exhaust pipe, it's a high-efficiency unit with a condensate drain. A clogged drain can trigger a safety shutoff. Look for standing water near the base of the unit.

If you've checked all of these and the furnace still won't heat, it's time to call.