Furnace Pressure Switch Stuck Open?

You want your house to be warm and cozy. You hear your basement machine turn on. The small fan motor starts to spin loudly. But the main gas fire never starts. The machine simply turns off after one minute. A furnace pressure switch stuck open is a very common safety warning. Your machine is trying to protect your family from bad air. We will help you find the blocked pipes and fix this problem fast.

The Safety Job

Checking Exhaust Air

Your heavy heater makes dangerous poison gas when it burns fuel. A small plastic fan motor pushes this bad gas out of your house through a metal or plastic chimney. The pressure switch is a small round disc that watches this fan. It has a tiny rubber hose that feels the air moving.

Stopping Poison Gas

If a bird builds a nest in your chimney, the bad gas cannot escape outside. The round switch feels the air stop. The switch stays open. An open switch tells the main computer to keep the gas valve completely closed. This stops your house from filling up with dangerous carbon monoxide. You must fix the airflow to close the switch. Check the EPA Indoor Air Quality page to learn about safe breathing air. You can also use our HVAC Calculators to see what size heating system your home really needs.

Common Causes For The Error

A Blocked Chimney Pipe

The most common problem is a blocked exhaust pipe. You need to walk outside your house and look at the white PVC pipes or metal vents coming from the basement. Thick winter snow or solid ice can cover the holes completely. Dead leaves and small sticks also blow into the pipes. You must clear all this trash away so the machine can breathe.

A Ripped Rubber Hose

Look closely at the tiny black rubber tube inside the machine. This small hose connects the round switch to the fan motor. The hot air inside the metal box makes this rubber very dry over time. The dry rubber cracks and gets tiny holes. The switch cannot feel the air moving if the hose has a hole. Read our Furnace Starts Then Stops guide to learn about these short cycles.

DIY Maintenance Tip

Clearing The Water Trap

Modern high efficiency machines create a lot of water when they run. This water drains out through small plastic tubes. Sometimes the drain gets completely clogged with green slime. The water backs up into the round pressure switch and ruins the inside parts. You can pull the black rubber hose off the switch and blow through it gently. This pushes the trapped water out. Check our Why Is My AC Leaking Water page for more help with clogged drain tubes.

Average Repair Costs

System Component	Main Purpose	Expected Lifespan	Estimated Part Cost	Estimated Labor Cost
Pressure Switch	Senses moving exhaust air	10 years	$20 to $50	$100 to $150
Rubber Tubing	Connects the air parts	5 years	$5 to $10	Free to do yourself
Draft Inducer Motor	Pushes bad air outside	10 years	$150 to $300	$300 to $600
Exhaust Vent Pipe	Carries poison gas away	20 years	$50 to $100	$150 to $250
New Gas Furnace	Replaces the whole unit	15 years	$800 to $1500	$1000 to $2000

When To Call A Pro

Testing The Vacuum

Sometimes the plastic switch just gets old and breaks inside. It stays open even when the air is blowing perfectly fine. A professional worker uses a special clear tube filled with red liquid to test the exact air pressure. This tool is called a manometer. It tells them if the chimney is blocked or if the switch is just dead.

Is your house freezing cold right now? Do you think a bird is stuck in your exhaust pipe? Our expert heating team can test your air pressure today. We carry brand new rubber hoses and round safety switches in our work trucks. We will fix your broken machine safely so your family stays warm.

FAQ

What does a furnace pressure switch stuck open mean?

It means the safety sensor does not feel the bad exhaust air leaving the machine so it stops the main fire from starting to protect your home.

How do I test the small rubber hose inside the heater?

You can gently pull the small black tube off the metal nipple and blow air through it to see if it has a crack or trapped water inside.

Can a dirty paper air filter cause this specific error code?

No, a dirty filter causes overheating problems but the round pressure switch only watches the exhaust chimney for dangerous carbon monoxide blocks.

How much does it cost to replace a bad pressure switch?

A professional heating worker will usually charge between $100 and $150 to buy a new plastic switch and install it safely in your basement.

Can I connect the two wires together to get heat tonight?

You must never connect the wires together to bypass this part because your house could fill up with deadly poison gas while you are sleeping.

Conclusion

A stuck safety switch keeps you safe from bad air. You must go outside and check your white exhaust pipes for thick snow or dead leaves. Look inside the machine for a cracked rubber hose. Clear any trapped water out of the plastic tubes. A professional worker can test the exact air pressure and install a new switch for about $150. Use our HVAC Services page to get safe heating help fast.