Why Is My Furnace Leaking Water?
Water around a furnace usually comes from a clogged drain on a high-efficiency furnace, a failed pump, or the AC coil that sits above it in summer. Look for standing water and a tripped safety switch first. If water is near the burners or the wiring, shut the furnace down.
What makes a furnace leak water?
Clogged drain or trap
A high-efficiency furnace squeezes so much heat out of the exhaust that it makes water every hour it runs in winter. When the trap or drain line clogs with slime, that water backs up and spills at the base. You can look for standing water and a tripped switch. Clearing the trap is a service visit.
Technician repairFailed water pump
Furnaces in basements often have to push their water uphill through a small pump. A stuck float or a burned-out motor lets the tank overflow onto the floor. You might hear the pump running all the time, or never. Testing and replacing it is technician work.
Technician repairThe AC coil above the furnace
In summer, the cooling coil that sits on top of the furnace makes the water, and a clogged coil drain sends it straight down through the furnace cabinet. If the leak only happens in cooling season, that drain is the suspect. Getting to it means opening the duct housing.
Technician repairHumidifier leak
Plenty of furnaces around here have a humidifier mounted on the ductwork with its own small water line. A stuck fill valve or a clogged humidifier drain drips steadily near the furnace. You can look at the humidifier and see where the water trail starts. The repair is ours.
Safe to check yourselfWater condensing in the flue pipe
On a standard furnace, exhaust that cools too much inside the metal flue turns back into water and drips down around the pipe. That usually means a venting problem, and the water is hard on the furnace. Venting work is strictly professional.
Technician repairLoose drain tubing inside the cabinet
Inside a high-efficiency furnace, several small hoses carry the water to the trap. Age and shaking loosen them, and you get drips that only show up while the furnace is running. Finding the loose hose means opening the cabinet, so that is our job.
Technician repairWhat can you check yourself?
- Note when the water shows up: only in winter, only in summer, or all year. That one detail narrows the cause more than anything else.
- Look for a tripped safety switch or standing water at the base of the furnace.
- Check the pump tank, if you have one, to see whether it is overflowing.
- Look at the humidifier and its small water line for drips.
- Mop up the water and keep it away from the wiring and the burners.
- If water is reaching electrical parts, switch the furnace off at the wall switch nearby.
Safety note: If water is pooling near the burners or any wiring, switch the furnace off and leave it off until it is checked. Never run a furnace that is wet inside.
When should you call for repair?
Call when the water keeps coming back after you mop it up, when the safety switch has tripped, or when you cannot tell where the water starts. Call before you run it again if water has reached the wiring, the burners, or the floor around stored belongings. Water inside the cabinet rusts the heat exchanger, the burners, and the control board. A small steady leak turns into a big repair if it is left alone.
Clarksburg holds the newest houses we work in, most of them built between the 2000s and the 2020s. High-efficiency furnaces came standard in them, and every one of those makes water all winter. The first fault on that builder equipment is usually small: a clogged drain, a water safety switch, or a control board. Whole developments like Arora Hills and Clarksburg Village went up over a short stretch, so these turn up together. Most of them are a repair, and we will say so.
Related questions
Why does my furnace leak water only in summer?
Summer water almost always comes from the air conditioning coil sitting on top of the furnace, not from the furnace itself. When that coil's drain or pan clogs, the water runs down through the furnace cabinet and pools at the base. The fix is in the AC drain. It still matters, because water running through a furnace rusts parts that were never meant to get wet.
Do high-efficiency furnaces normally make water?
Yes. A high-efficiency furnace pulls so much heat out of the exhaust that the moisture in it turns back into water. That water should leave through a trap and a drain line. Several gallons a day in cold weather is normal. What is not normal is seeing any of it outside the cabinet.
Is a leaking furnace dangerous?
The water itself is only water. Where it sits is the risk. Water reaching the wiring or the control board can short parts out, and long-term damp rusts the burners and the heat exchanger. If the water is anywhere near electrical parts or the burners, switch the furnace off. Otherwise contain it and book a repair.
Can I keep running a furnace that is leaking water?
If the water is minor, away from electrical parts, and you have a visit booked, running it for heat in the meantime is usually all right. Check the area often. If the puddle grows, the safety switch trips, or water reaches the wiring or the burners, shut it down. Warmth is not worth rusting a heat exchanger.
If water keeps showing up around your furnace, call Mora Heating & Air and we will trace it to the source.
Or tell us what your system is doing
Send us the details and we will call you back. If the house is very hot or very cold right now, calling is faster.