The short answer
When a Payne furnace in Northern Virginia flashes 31, the board is telling you the draft wasn’t proved. Before the gas can open, the inducer motor has to pull exhaust through the furnace hard enough to close the pressure switch. If it doesn’t close, nothing lights. The cause is usually a plugged condensate drain, a blocked vent, or a cracked or water-filled tube. The switch itself is the last suspect, not the first.
What you’ll notice
- The small motor on top (the inducer) starts and runs, but the igniter never glows and nothing lights.
- After a while it stops, waits, and tries again.
- The light flashes 3 short and 1 long. A Payne with a display shows 31, or 31.4 or 31.5.
- On a high-efficiency furnace you may hear gurgling in the drain hose, or see water where it shouldn’t be.
The $67 Heating Check
We check your furnace, heat pump or boiler before winter. Through December 31. See the offer
How to read the code
Look through the small window in the lower door. Short flashes are the first digit and long flashes are the second, so 31 is 3 short and 1 long, then a pause before it repeats. Payne’s PG80MSU and boards like it also show a three-digit code on a small display: the first two digits are the flash code and the third narrows it down, like 31.4. They keep the code through a power cut, and a technician can pull the last 7 faults from the board’s memory. Older Payne furnaces with a red light, like the PG9MAA, erase the code the moment the power goes off, so count it before you open the door or flip the switch. A steady light is normal, and rapid flashing means the line voltage polarity is reversed.
Two kinds of Payne furnace, two ways of proving the draft
Payne proves the draft two ways, and which furnace you have changes what 31 means.
Swipe to see all columns →
Swipe to see all columns →
| PG9MAA (condensing, 90%+) | PG80MSU (80%) | |
|---|---|---|
| Vent | White PVC pipes out the wall or roof | A metal vent into a chimney or flue |
| Draft proof | A pressure switch with rubber tubes | A pressure sensor that reads the draft |
| Code light | A red light; the code erases on a power cut | An amber light plus a display; keeps the last faults |
| What 31 means | The pressure switch didn’t close, or opened during the heat call | The prepurge and igniter warm-up didn’t finish within 5 minutes; it tries again after 2 minutes |
The PG80MSU narrows it down further. 31.4 and 31.5 mean the draft pressure dropped out before or after the blower came on. 14.4 is a lockout after 7 losses of pressure in one heat call. 23.3 means the board saw pressure when it shouldn’t have any, which points at the sensor or its tubing. Our full list of Payne furnace codes has the rest.
What usually causes it
- A plugged condensate drain. A condensing furnace makes water as it heats. When it can’t drain, it backs up into the collector box and the switch can’t read the draft. Common in winter, especially when a drain line runs through a cold spot.
- A cracked, loose or water-filled tube. On the PG9MAA, the pressure switch tube has a pink label and the relief port tube a green one. On a downflow or horizontal install, the relief port tube connects to the switch too. A tube that’s split, kinked or full of water reads wrong.
- A blocked vent or intake. Snow, ice, leaves, a nest, or a sagging pipe that holds water.
- A weak inducer motor. It runs, but not hard enough to pull the draft the switch needs.
- The switch itself. It does fail, but we test it last, after the things that make a good switch read bad.
What you can safely check
- Count the code and write it down. On a PG9MAA, do that before you touch the power, because a power cut erases it.
- Outside, look at the vent and intake pipe ends. Clear snow, ice and leaves from around them, and don’t push anything into the pipe.
- Find the condensate hose and pump beside the furnace. A pump full of water that isn’t running, or a hose that’s kinked or frozen, is your lead.
- Look at the small rubber tubes on the pressure switch for a crack, a kink or a loose end. Don’t pull them off.
- Turn the furnace switch off for 30 seconds, back on, and let it try once.
How Payne has a technician test it
Payne’s PG9MAA manual has a check for the switch itself, and it’s a technician’s test. With the power off and the door off, the inducer’s wires come off. The power goes back on with a call for heat. After a minute, the igniter must not glow and the light should flash 31. If the igniter glows, the switch is closing when it shouldn’t, and the furnace gets shut down at once. Then the inducer gets reconnected. It’s live voltage on a gas appliance, so it’s our job, not yours.
What not to do
Never jump or bypass a safety switch to get heat back. Each one is there to stop the furnace from burning gas when something is wrong, and the wrong thing is often exhaust, which carries carbon monoxide. If you smell gas, don’t flip any switches: leave the house and call your gas company or 911 from outside.
What a technician does
We read the draft with a manometer and compare it to the rating printed on the switch, clear the drain and the trap, check every tube and the vent, and watch the inducer pull. If everything else checks out and the switch still won’t close, we replace it with one that matches the rating, and you get the price before the part goes in.
What it costs to have us look
A repair visit starts with a flat $99 diagnostic, and you get the price of the fix before we touch anything. Payne is made by Carrier, so our Carrier repair page lists what the common furnace repairs cost. Our heating check is $67 per system, through December 31: furnace, heat pump or boiler.
- Every Payne furnace code and what to do
- The Carrier pressure switch, the same design
- The Goodman pressure switch
- A clogged or frozen furnace condensate drain
- Every Carrier furnace code, since Carrier makes Payne
Every code meaning here comes from Payne’s own documents: PG80MSU installation and service manual and PG9MAA installation instructions.
Call or book
Call (703) 997-9757 and tell us the code you counted, or book online from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
What does code 31 mean on a Payne furnace?
The draft wasn’t proved. On a PG9MAA, the pressure switch didn’t close or opened during the heat call. On a PG80MSU, the prepurge and igniter warm-up didn’t finish within 5 minutes. Either way, the gas won’t open until the draft is proved.
Why does my Payne furnace inducer run but nothing lights?
The board is waiting for the pressure switch to close. Until it does, the igniter stays off and the gas stays closed. A plugged drain, a blocked vent or a bad tube are the usual reasons.
Can a clogged drain cause a pressure switch error?
Yes, on a condensing furnace. Water backs up into the collector box and the switch can’t read the draft. Clearing the drain often clears the code.
Should I replace the pressure switch myself?
No. A new switch on a furnace with a plugged drain or a weak inducer throws the same code the next day. It gets tested first and replaced last, with one that matches the rating on the label.
How much does it cost to have a Payne pressure switch looked at?
A repair visit starts with a flat $99 diagnostic, and you get the price of the fix before any work starts. Our heating check is $67 per system, through December 31.
