What the pressure switch does
Before the furnace is allowed to light, the inducer motor runs and creates negative pressure in the vent system. A small diaphragm switch, connected by a rubber hose, senses that pressure and closes its contacts, telling the control board the vent path is clear. If the switch does not close, the furnace will not ignite. That is a deliberate safety design to prevent combustion products from spilling into your home.
Why the switch does not close
| Cause | How common in Buffalo | What to look for |
|---|---|---|
| Snow or ice over the outdoor PVC terminations | Very common in lake-effect season | Drifted snow at the sidewall vent pipes |
| Clogged or frozen condensate drain | Very common in cold basements | Water pooling at the furnace base; full condensate pump |
| Cracked, kinked, or disconnected sensing hose | Common | Visible hose damage at the switch |
| Debris in the vent — leaves, nests, insulation | Occasional | Seasonal, often after fall or spring |
| Failing inducer motor | Occasional | Weak, noisy, or slow inducer operation |
| Blocked inducer port or corroded pressure tap | Occasional | Requires disassembly to see |
| Genuinely failed switch | Least common | Confirmed only after everything else is ruled out |
Safe checks a homeowner can do
- 1
Go outside and look at the vent pipes
Two PVC pipes on an exterior wall, usually 12–24 inches above grade. Clear at least a foot of space around them by hand or with a broom — never with a shovel against the pipe.
- 2
Check for ice at the pipe ends
Exhaust condensation can build an ice collar in extreme cold. Clear it gently; do not chip at the pipe itself.
- 3
Look at the condensate drain and pump
If the pump reservoir is full or water is pooling around the furnace base, that is very likely your cause.
- 4
Replace the filter
Rules out a contributing airflow issue before the call.
- 5
Note the error code
Most boards flash a specific count for a pressure switch fault. Tell us the pattern.
Where safe checks end
Never bypass a safety switch, open or adjust a gas valve, disassemble burners or the heat exchanger, jump control board terminals, or work on live wiring. If the safe checks below do not restore heat, stop and call 716-412-2677.
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The Buffalo winter pattern
Lake-effect bands off Lake Erie can dump a foot or more of snow in hours across parts of South Buffalo, West Seneca, Hamburg, and Orchard Park while other neighborhoods get little. Sidewall vent terminations disappear under drifts quickly, and plows and roof runoff make it worse. The furnace shuts down, the homeowner assumes a major failure, and the actual cause is a pipe under a snowbank.
The other seasonal pattern is condensate freezing. A condensing furnace can generate several gallons of water a day, and any portion of that drain line running near an unheated basement wall, a crawl space, or an exterior discharge point can freeze during a hard cold stretch. Insulating vulnerable runs and rerouting an exterior discharge to an interior drain are both practical preventive fixes.