Ruud U802VA050317MSA Error Code T045_F: Inducer Lo Pressure Switch Won't Close
What Does Code T045_F Mean?
Before the Ruud U802VA lights, the inducer (draft) motor spins up to pull combustion air through the heat exchanger and push exhaust out the vent. The low-stage pressure switch is a safety device that watches for the negative pressure that proper draft creates; it must close to tell the Bluetooth Communicating IFC that the exhaust path is clear before the control will open the gas valve and energize the igniter. T045_F is logged when the inducer is running but that switch does not close within 60 seconds. The 'T' prefix means the control is treating this as a transient (intermittent) failure to prove draft.
This code is the mirror image of A044_F on the same board. A044_F is 'Inducer Lo Pressure Switch Won't Open' — the switch stays closed when the inducer is OFF, when it should be open. T045_F is the opposite: the switch stays open when the inducer is ON and should have closed. Because it is a failure to prove draft, the safety logic will not allow ignition. If the switch keeps failing to close, the control counts the 60-second timeout and steps the furnace into a five-minute soft lockout, which is reported as the T047_F / A047_F 'Inducer Fan 5 Minute Lockout' condition.
The reason this is often a homeowner fix is that the most common cause sits outside the house. The U802VA is an 80% furnace that vents its exhaust to a termination outdoors, and a partial or full blockage there — packed snow, an ice cap after a thaw-freeze, leaves, or a bird or rodent nest — reduces draft enough that the pressure switch never sees the negative pressure it needs. Less common causes are internal and not DIY: a weak or failing inducer motor, or a cracked, disconnected, or water-filled pressure-switch hose. Clearing the outside terminal is the safe first move; the internal parts are technician work.
What You'll Notice
- The inducer motor audibly spins up at the start of a heat call, but the burners never light.
- After about a minute the furnace goes quiet, then retries a few minutes later (the soft-lockout retry).
- No heat is delivered even though you can hear the draft fan running.
- The contractor app logs T045_F, often followed by T047_F/A047_F five-minute lockout entries.
- Outside, the vent or intake terminal is capped with snow or ice, clogged with leaves, or has a nest in or near it.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked vent or flue pipe | Most common | ✓ DIY fix → |
| Weak or failing inducer motor | Common | ✗ Call a pro → |
| Cracked or disconnected pressure switch hose | Common | ✗ Call a pro → |
How This Is Diagnosed
The logical order starts outside and moves in. First the vent and intake termination are checked for snow, ice, debris, or nests, since a restricted exhaust path is the most common reason the switch cannot prove draft. If the outside terminal is clear and T045_F still logs, the problem is internal: the inducer motor's output is measured, and the pressure-switch hose is inspected for cracks, disconnection, or condensate blockage before the switch itself is tested. Those internal checks are technician work and are not safe DIY tasks.
How to Fix It: Clear the outside vent and intake terminal
What You'll Need
Steps
- Shut off power and gas first Turn off power to the Ruud U802VA at the breaker or the furnace switch, and shut off the gas supply valve at the furnace. If you smell gas, leave immediately and call your gas company. Do not continue until both power and gas are off.
- Find the outdoor vent/intake termination Go outside and locate the furnace's vent (and intake, if present) where it terminates through the wall or roof. On this 80% furnace it carries combustion exhaust, so a blockage directly starves the draft the pressure switch needs to close.
- Gently clear any blockage Remove snow, ice, leaves, or a bird/rodent nest from the terminal and the area immediately around it. Use a soft brush or your gloved hand — do not jam anything down the pipe or use force that could crack it. Make sure nothing is drifting back over it (for example, snow piling up from a plow or roof runoff).
- Restore gas and power and run a heat cycle Turn gas back on, restore power, and call for heat. Listen for the inducer to spin up and the burners to light within the normal proving window.
When to Call a Professional
Contact a licensed HVAC technician if:
- T045_F keeps logging after the outdoor vent and intake terminal are confirmed clear.
- The furnace steps into repeated T047_F or A047_F five-minute lockouts.
- The inducer sounds weak, noisy, or slow to spin up, or you suspect it is not reaching full speed.
- You see a pressure-switch hose that is cracked, disconnected, kinked, or holding water — do not attempt to service the hose or switch yourself.
Frequently Asked Questions
Why does my Ruud U802VA show T045_F only on cold or snowy mornings?
Snow drifting over the vent terminal, or an ice cap forming after a thaw and refreeze, is a classic cause. It restricts the exhaust path just enough that the low-stage pressure switch cannot prove draft. Clearing the terminal usually resolves it; keep the area around it clear during winter.
What is the difference between T045_F and A044_F?
They involve the same low-stage pressure switch but opposite failures. A044_F is 'won't open' — the switch stays closed with the inducer off. T045_F is 'won't close' — the switch stays open with the inducer running, so the furnace cannot prove draft and will not light.
The vent looked clear but T045_F keeps coming back — is it safe to keep resetting it?
If the outside terminal is genuinely clear and the code persists, the cause is internal — a weak inducer motor or a cracked, disconnected, or water-filled pressure hose. Those are not homeowner repairs, and repeatedly resetting a furnace that cannot prove draft is not advisable. Have a technician inspect the inducer, hose, and switch.
✓ Verified against manufacturer service manual — March 2026