Rheem Furnace Leaking Water: Causes, Fixes & Costs
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Rheem furnace leaking water: what it means
“Leaking water” is a symptom, not a flash code. No Rheem control board reports a leak directly.
Most leaks happen on Rheem’s 90%+ condensing furnaces. These units pull so much heat from the exhaust that water vapor condenses inside the secondary heat exchanger. That slightly acidic water drains through the collector box and a trap, then out to a floor drain or a condensate pump. A leak means one of three things:
- The drain path is blocked.
- A drain part is disconnected or cracked.
- The water is coming from something else, such as the AC coil, a humidifier, or the vent pipe.
A blocked drain often shows up on the furnace as well. Many Rheem condensing models will flash a pressure switch fault, because water backing up in the collector box or inducer trips the switch.
- Reset behavior: Typical Rheem boards retry after a pressure switch trip. Some go into a timed soft lockout, often about an hour. The exact code and behavior vary by board, so check the label on the blower door.
- The leak itself won’t clear on its own. Fixing it means finding where the water comes from.
Rheem furnace leaking water: common causes, ranked by probability
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Clogged condensate drain line or trap. This is the most common cause on condensing models. Algae, sludge, and debris from the heat exchanger build up in the trap and hose. Water then backs up and spills out of the cabinet.
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Failed or unplugged condensate pump. When there is no floor drain nearby, a small pump lifts the water away. Common failures:
- The float sticks.
- The motor dies.
- The check valve clogs.
- The pump gets unplugged.
When any of these happen, the reservoir overflows.
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Disconnected, cracked, or misrouted drain hoses. Hoses inside the cabinet can slip off after service, kink, or crack with age. On some models, the trap and hoses must be reconfigured when the furnace is installed in a different orientation, such as upflow, downflow, or horizontal. If that wasn’t done correctly, water leaks inside the cabinet.
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Air conditioner evaporator coil overflow. The coil sits on top of the furnace. A clogged coil drain or a rusted pan sends water down through the furnace. This is the most likely cause if the leak happens during cooling season.
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Frozen drain line. This happens in attics, crawlspaces, and garages, and with drain lines routed outdoors. Ice blocks the line and water backs up.
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Vent pipe condensation draining back. This can happen on condensing models with incorrect PVC slope or no drain tee. It can also happen on 80% models vented into an oversized or unlined masonry chimney, where flue gases condense and run back into the furnace.
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Humidifier leak. A furnace-mounted humidifier with a clogged drain, a stuck solenoid valve, or a cracked supply line can drip onto or into the furnace.
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Cracked collector box, leaking inducer seal, or failed secondary heat exchanger. These are less common, but they are serious. Acidic condensate is then escaping inside the cabinet. The heat exchanger is often covered by Rheem’s limited warranty, but labor usually is not.
How to fix Rheem furnace leaking water: safe checks first
If water is near wiring or spreading, turn the furnace off first. Use the service switch next to the unit or the breaker. Then work through these checks:
- Note when the leak happens.
- A heating-only leak points to the furnace’s condensate system.
- A cooling-only leak points to the AC coil.
- A leak in both seasons points to a shared drain line or pump.
- Check the condensate pump.
- Make sure it is plugged in and the outlet works.
- If the reservoir is full and the pump won’t run, it has likely failed. Leave the furnace off and call for service.
- Check the end of the drain line.
- Find where the line ends, at a floor drain, outdoors, or at a standpipe.
- Make sure it isn’t kinked, crushed, or frozen.
- You may clear a clog at the open end with a wet/dry vacuum.
- Look at the visible drain tubing outside the cabinet. Check for hoses that have obviously fallen off the drain or the pump. Note what you see, but don’t open the furnace panels to reconnect anything.
- Check the filter. A very dirty filter can make the AC coil freeze and then flood during cooling season. Replace the filter if it’s dirty.
- Look at the humidifier. If you have one and see water dripping from it, close its water supply saddle valve. That valve is outside the furnace.
- Reseat the front panels. Make sure they are fully seated after any service. Use the furnace’s single reset only once, after the water source has been stopped.
Do not open the burner or blower compartments to clean the internal trap. Do not pour chemicals into the furnace.
How a technician will diagnose it
A good technician will usually take these steps:
- Read the board’s fault code and history. Look for pressure switch trips.
- Trace the water to its source: furnace trap, collector box, inducer, vent, AC coil pan, or humidifier.
- Remove and flush the condensate trap and hoses. Confirm the trap is primed and set up correctly for the furnace orientation, following the Rheem installation manual.
- Test the condensate pump’s float, motor, and check valve, and its overflow safety switch if it has one.
- Check the slope of the PVC vent and intake pipes, and check vent drain tees. On 80% units, check the chimney liner sizing.
- Inspect the inducer housing and collector box for cracks or failed gaskets.
- If corrosion or a leak suggests a failed secondary heat exchanger, inspect it and check warranty status using the serial number.
- Inspect the evaporator coil pan and coil drain line.
Red flags on a quote:
- Recommending a heat exchanger replacement without showing you the leak point.
- Recommending a new furnace for what turns out to be a clogged trap.
Symptom, cause and what to do
| Symptom | Likely cause | DIY action | Technician job |
|---|---|---|---|
| Water under furnace in winter, furnace cycling or flashing a code | Clogged trap or drain line | Check the outlet end of the drain line; turn the furnace off if water is spreading | Remove and flush the trap and hoses, re-prime the trap |
| Pump reservoir full, pump silent | Failed or unplugged condensate pump | Confirm the pump is plugged in and the outlet works | Replace the pump or its check valve |
| Leak only during AC season | Evaporator coil pan or drain clog | Replace a dirty filter; check the coil drain outlet | Clear the coil drain, replace a rusted pan |
| Leak after recent service or reinstall | Hose off, or trap set up wrong for orientation | Note visible disconnected tubing | Reconnect hoses, reconfigure the trap per the manual |
| Water dripping from the vent pipe connection | Vent slope or condensation drainback | None beyond noting it | Re-pitch the vent, add a drain tee, or reline the chimney |
| Drip from a unit mounted on the furnace | Humidifier leak | Close the humidifier water supply valve | Repair the drain or solenoid, or replace the pad |
| Rust or water inside the cabinet near the inducer | Cracked collector box or failed secondary heat exchanger | Shut the furnace down | Diagnose, file a warranty claim, replace parts |
| Leak with an attic or garage drain in freezing weather | Frozen drain line | Thaw only the accessible exterior line, gently | Reroute, insulate, or add heat tape |
Rheem furnace leaking water repair cost
These are typical US ranges, including labor:
| Repair | Typical cost |
|---|---|
| Service call and diagnosis | $80–$200 |
| Flush trap and drain lines | $100–$250 |
| Condensate pump replacement | $150–$400 |
| Hose or trap replacement, or reconfiguration | $120–$300 |
| AC coil drain clearing | $100–$250 |
| AC coil drain pan replacement | $250–$700 |
| Vent re-pitch or drain tee | $150–$500 |
| Chimney liner for an 80% model | $800–$2,500 |
| Humidifier repair | $100–$350 |
| Collector box or inducer seal | $250–$700 |
| Inducer replacement | $400–$900 |
| Secondary heat exchanger, part under warranty | $600–$1,500 labor |
| Secondary heat exchanger, out of warranty | $1,500–$2,500+ (replacing the furnace may then be worth considering) |
Related codes
Rheem Furnace Keeps Shutting Off: Causes & Fixes (a blocked drain often causes pressure switch shutdowns)
Rheem Furnace Short Cycling: Causes, Fixes & Costs
Rheem Furnace Won’t Ignite: Causes, Fixes & Costs
Rheem Furnace Ignition Lockout: Causes, Fixes & Costs
Rheem Furnace Won’t Turn On: Causes, Fixes & Costs
Frequently asked questions
Is it normal for a Rheem furnace to produce water?
Yes, if it is a 90%+ high-efficiency model. These furnaces condense water from the exhaust gases, sometimes several gallons a day in cold weather. That water should leave through the drain line or condensate pump. It should never pool on the floor.
Can I keep running my furnace while it leaks?
Only briefly, and only if the leak is small and away from wiring. Water can damage the control board and inducer, and it can cause pressure switch faults. If water is reaching electrical parts or spreading, turn the furnace off at its service switch and call a technician.
Why does my furnace leak only in summer?
A summer leak usually comes from the air conditioner's evaporator coil above the furnace, not from the furnace. The coil's drain pan or drain line clogs or overflows, and the water runs down through the furnace cabinet.
Will a clogged drain stop my Rheem furnace from heating?
Often, yes. On many condensing models, water backing up into the inducer or collector box opens the pressure switch. The board then flashes a pressure switch code and stops the ignition sequence. The exact flash code and the retry or lockout behavior depend on the board, so check the code label on your unit's door.