Furnace Pressure Switch Problems: No-Heat Guide for furnaces

If your furnace isn’t working, your thermostat is calling for heat, and you see a pressure switch error code blinking on the furnace, you’re not alone. This is one of the most common no-heat calls we see in Edmonton, Stony Plain, Spruce Grove, and Parkland County.

In this guide, Over the Top Heating explains, in plain language:

• What a furnace pressure switch actually does

• Why it’s so important for furnace safety in Alberta

• The most common causes of pressure switch problems

• What homeowners can safely check themselves

• When it’s time to call an HVAC technician for furnace repair

What Is a Furnace Pressure Switch?

A furnace pressure switch is a small but critical safety device inside your gas furnace. Its job is to make sure your venting system is actually moving exhaust out of the home before the burners light.

On a typical high-efficiency furnace in an Edmonton home, here’s what happens when there’s a call for heat:

1. Your thermostat calls for heat.

2. The inducer motor (small fan at the top of the furnace) starts running.

3. As the inducer moves air, it creates a certain pressure or vacuum in the vent pipes.

4. The pressure switch “proves” the venting by measuring that pressure.

5. If everything looks safe, the pressure switch closes and tells the furnace’s control board, “We’re good to go—light the burners.”

If the pressure switch doesn’t see the right pressure, it stays open, and the furnace refuses to fire. That’s why you end up with no heat but a flashing pressure switch error on the control board.

In other words, the pressure switch is the furnace’s way of saying:

“If I can’t vent safely, I’m not turning on.”

Why Is the Pressure Switch So Important for Safety?

In homes across Edmonton and Parkland County, a properly working pressure switch helps prevent:

• Exhaust gases from backing up into the furnace and home

• Potential carbon monoxide exposure

• The furnace running with blocked or restricted venting

• Damage to the furnace from poor combustion or overheating

If the pressure switch is tripping, it’s not trying to annoy you—it’s trying to protect your family.

Common Causes of Furnace Pressure Switch Problems

Most of the time, the pressure switch is reacting to another problem in the system. Here are the most common reasons we see on furnace repair calls in Stony Plain, Spruce Grove, and Edmonton.

1. Blocked Furnace Vent or Intake

High-efficiency furnaces use plastic (636/PVC) vent pipes that run outside. Those pipes can easily be blocked by:

• Heavy snow or drifting snow piles

• Ice buildup around the termination

• Leaves, dirt, or debris

• Bird nests, wasp nests, or small animals

• Toys or objects placed near the vent termination

When the vent or intake is blocked, the inducer can’t move air properly, the furnace can’t establish the right pressure, and the pressure switch won’t close. That leads to a no-heat situation and a pressure switch error code.

2. Condensate Drain Problems (High-Efficiency Furnaces)

Most high-efficiency furnaces in Edmonton produce condensate water that drains away through a small hose, trap, or condensate pump.

If that drain:

• Gets plugged with dirt or slime

• Has low spots that hold water

• Runs through a cold space and freezes

…water can back up into the inducer housing or pressure tubing, causing the pressure switch to trip and shut the furnace down.

3. Weak or Failing Inducer Motor

The inducer motor has to pull a specific amount of air through the venting system. If it’s:

• Worn out or seizing up

• Making unusual noises (whining, grinding, rattling)

• Rusted or collecting water

…it may not create enough pressure for the switch to close, and you’ll keep seeing a pressure switch open error.

4. Cracked, Loose, or Plugged Pressure Tubing

The pressure switch is usually connected to the furnace by a small rubber or silicone tube.

Common issues we see:

• Cracks or splits in the tubing

• Loose connections that leak air

• Water trapped inside the tube

• Spider webs or debris plugging the port

Any of these can give the pressure switch the wrong reading and cause a furnace lockout.

5. Actual Pressure Switch Failure

Sometimes the pressure switch itself is worn out. Over time, the internal diaphragm or contacts can fail. The furnace inducer and venting might be working perfectly, but the pressure switch simply never closes.

A proper HVAC diagnosis will confirm whether the switch is bad or whether another issue is causing the fault.

What Homeowners Can Safely Check (Before Calling for Furnace Repair)

There are a few safe checks most homeowners around Edmonton and Stony Plain can do before calling for emergency furnace repair.

?? Important: If you ever smell gas, feel unwell, or suspect carbon monoxide, shut the furnace off and contact a professional immediately.

1. Check the Outdoor Vent and Intake

Step outside and find the furnace vent and intake pipes:

• Make sure they’re not buried in snow.

• Clear away ice, frost, or debris.

• Don’t add screens, cloth, or makeshift covers that can plug with frost.

If you clear a blockage and the furnace runs normally afterwards, that might be the immediate fix—but if the problem keeps returning, it’s time for a professional inspection.

2. Check and Replace the Furnace Filter

A very dirty filter can affect furnace performance and may contribute to safety lockouts.

• Slide the furnace filter out.

• If it’s plugged or older than 2–3 months, replace it.

• Make sure you install the correct size and airflow direction.

Even if this doesn’t completely fix the pressure switch error, it’s a good first step in any furnace troubleshooting.

3. Look for Water Around the Furnace

On a high-efficiency furnace:

• Look around the base for water pooling.

• Check the condensate pump (if you have one) to ensure it’s plugged in and not overflowing.

• Visually inspect the condensate lines for big sags or obvious blockages.

Don’t start cutting or taking things apart, but note anything unusual. This information really helps your HVAC technician from Over the Top Heating when they arrive.

What You Should Not Do With a Pressure Switch Error

There are a lot of “quick fixes” online that are not safe for your home heating system:

• Do not bypass or jump the pressure switch to force the furnace to run. This disables a key safety device and can allow dangerous conditions.

• Do not drill holes in the venting or modify vent lengths yourself. Venting must meet Alberta gas codes and manufacturer specs.

• Do not keep resetting the furnace over and over if it keeps locking out. Repeated lockouts mean the furnace is telling you something is wrong.

If you’re unsure, shut the furnace off and call a qualified Edmonton HVAC company like Over the Top Heating.

When to Call a Furnace Repair Expert in the Edmonton Area

You should book a furnace service call if:

• You have no heat and a pressure switch or venting error code

• You’ve already checked the outside vents and filter

• You hear strange noises from the inducer or blower

• You notice water leaking around the furnace or venting

• The furnace keeps starting then shutting down after a few seconds

A licensed tech from Over the Top Heating will:

• Measure vent pressure with proper tools

• Test the inducer motor amperage and performance

• Inspect and clear exhaust and intake venting

• Check and flush the condensate drain system

• Test the pressure switch and wiring

• Make sure everything meets Alberta safety codes and manufacturer requirements

Can a Furnace Pressure Switch Be Repaired?

In most cases, pressure switches are replaced, not repaired.

A proper diagnostic from an HVAC professional will:

1. Rule out venting, drain, or inducer problems.

2. Confirm if the pressure switch is truly defective.

3. Replace it with the correct, furnace-specific part.

4. Test the furnace through several full heat cycles.

This helps avoid throwing parts at the problem and ensures your furnace heating system is safe and reliable.

Preventing Future Pressure Switch Problems

You can’t prevent every furnace breakdown, but you can dramatically lower the chances of a pressure switch error with simple preventative steps:

• Schedule annual furnace maintenance with a licensed HVAC technician.

• Keep outdoor vents clear after snowfalls & storms.

• Replace your furnace filter regularly during heating season.

• Watch for any water leaks or odd noises and deal with them early.

FAQ: Furnace Pressure Switch Questions (For Homeowners)

1. What does a furnace pressure switch do?

The pressure switch makes sure your furnace can move exhaust safely through the venting before the burners fire. If the venting or inducer isn’t working properly, the switch stays open, and your furnace shuts down to protect you.

2. Why does my furnace say “pressure switch open”?

This usually means your furnace couldn’t create the right vent pressure. Common causes include blocked vents, condensate problems, a weak inducer motor, damaged pressure tubing, or a failed pressure switch.

3. Can I bypass a furnace pressure switch to get heat?

No. Bypassing the pressure switch is unsafe. It disables a critical safety device and can allow your furnace to run in dangerous conditions, including potential carbon monoxide risks.

4. How do I know if my furnace vent is blocked?

Signs include repeated pressure switch errors, the furnace starting and shutting off quickly, or visible snow/ice/debris around the vent termination. If you’re not sure, have a professional inspect it.

5. When should I call Over the Top Heating?

Call us if:

• Your furnace is showing a pressure switch or vent error

• You have no heat in your home

• You notice water around the furnace

• The furnace keeps locking out or acting inconsistently

We provide furnace repair and HVAC service in Stony Plain, Spruce Grove, Parkland County, and Edmonton, and we’re happy to help diagnose and fix furnace pressure switch problems safely.