If your high-efficiency furnace is leaking water, it's most often a problem with the condensation pipes. In a high-efficiency furnace, the air inside the heat exchangers will become cold enough to produce condensation. When operating normally, the condensation will drip down into a drain pan. From there, it will drain outside your home through your furnace's condensation pipes.
When there's a problem with the condensation pipes, however, it causes the condensation to leak onto your floor instead. Read on to learn more about what can cause a high-efficiency furnace to leak and how you can stop it.
Clogged Condensation Trap
In most cases, a leaking high-efficiency furnace is caused by a clog in the condensation trap. The trap is a U-shaped bend on your condensation pipe, and it will be flanked by an uncapped vent pipe on the downstream side and a capped clean-out pipe on the upstream side. The condensation trap collects water, which prevents harmful exhaust gases from coming out of the vent pipe. Unfortunately, it can trap debris as well. Once it's clogged, water will back up through the condensation pipes and out through the furnace's drain pan.
Thankfully, it's easy to clean out your condensation trap with a wet/dry vacuum. Turn the power to your furnace off to prevent it from venting exhaust gases while you're cleaning it, and then attach the wet/dry vacuum to the end of the condensation pipe outside your home. Turn the vacuum on, go back inside your home and remove the cap from the clean-out pipe.
Pour water down the clean-out pipe to flush out any clogs in the condensation trap. For stubborn clogs, you may need to use vinegar or warm water. Don't use boiling hot water, since high temperatures can damage your PVC condensation pipes.
If you can't remove the clog with water, you can try using a toilet snake. You'll need to feed the snake into the clean-out pipe and attempt to pull the clog out. Once you've removed the clog, condensation will stop backing up into your furnace's drain pan.
Malfunctioning Condensation Pump
In order to carry condensation away from your furnace, the condensation pipes need to slope slightly downwards as they exit your home. Unfortunately, this isn't always possible when installing a new high-efficiency furnace. If condensation needs to be carried uphill, a condensation pump will be installed on that section of your condensation pipes. It acts like a small sump pump that pushes water further along the pipes.
If you don't hear the condensation pump running when the furnace is turned on, then its motor may have failed. This causes water to back up and leak onto the floor. You'll need to call a heating service to have the condensation pump inspected and replaced.
Frozen Condensation Pipe
If the outdoor portion of your condensation pipe is frozen, water will back up through the pipe and onto your floor. If you notice ice in the outside section of pipe, soak a towel in hot water and then wrap it around the pipe. This will melt the ice and allow condensation to flow freely out of the pipe again.
Leaking Condensation Pipe
Finally, your condensation pipe may simply be leaking. Like your plumbing pipes, the PVC pipes used in your furnace's condensation pipes can develop leaks. If you notice any cracks in the pipes or if the outside of the pipes are wet, you should suspect a leak. You'll need to call a heating service technician to have the broken sections of pipe replaced.
Overall, issues with a high-efficiency furnace's condensation pipes are typically easy to fix. If the leak is due to a clog in the condensation pipe, you can often remove it on your own. However, you'll need to call a heating service if the pipes are leaking or if the condensation pump has failed.
If you can't find out what's causing your high-efficiency furnace to leak, have a heating service come out to inspect the problem—water leaks should be fixed immediately, since they can lead to mold or damage to the electrical components on your furnace.