Got called by my wife while at work last week, house was cold and furnace not running. Walked her through checking the thermostat, breaker, and switch, all fine. Have to try and sort out when I get home. Realized the humidifier had not power as well, started tracing some lines and bumped the condensate pump, which ran and suddenly the furnace gets power and everything runs as normal. Hooray, I thought. Happened again two days later, though now I knew where to go. Bumped the pump, it ran, and all is well. The pump is has an internal cut off switch to prevent the furnace/A/C from running if it is full above where it should be running. After I got the house back to normal temp, I removed the condensate pump to check it out, discovered a ton of mold/bacteria biofilm which appeared to be weighing down the float switch, thus preventing it from running. Cleaned it all out, and it has been working normally for the past week with no further failures. Problem solved, now, how do I prevent that mold growth from happening again?

To keep mold from growing in my A/C condensate line I pour in about a quart of bleach water every time I change the air filter in the summer months. It has worked for me.

Not familiar with the set up but was having mold issues in my A/C unit and installed a UV / BLACK light. UV light seems to break down the mold.

There are tablets you can buy that dissolve very slowly to prevent growth.

Check Amazon

Our AC technician told us to pour some Simple Green into the drain pipe once per month.

"Condensate pump?" I'm confused. Running the AC results in condensate, not the furnace. And, I don't know about yours, but ours has no pump. The condensate drops to a pan under the evaporator in the furnace plenum, drains out the back, and into a drain pipe.

Are you perhaps talking about a whole-house humidifier reservoir float switch?

Our condensate drain line also serves the humidifier. Every year, when I change the humidifier evaporator pad, I plug the end of the condensate drain line, fill the line with a 50/50 mix of vinegar and hot water, let it sit for five minutes, then pull the plug.

Our humidifier has no reservoir or float switch. Water runs continuously over the pad during the furnace's heating cycle, with the excess draining out the bottom, into the drain line.

Quarter cup of bleach in drain line every month or so in high humidity season. The line typically has a trap so clogs build up fast. For the OP's condensate pump, do the same. If the line has not cleared, a wet vac adapted to the end of the drain line usually clears it.

quote:

Running the AC results in condensate, not the furnace.

Water is a byproduct of combustion.
Maybe not as much as A/C condensation but it is there and also is acidic/corrosive.
I'd second the bleach although it doesn't take a lot to maintain.
Clearing the initial clog may require mechanically removing the blockage.

For those that really want to know more:

https://www.sciencedirect.com/...ii/S036054422103317X

I've also learned to keep a backup condensate pump on hand (they aren't expensive) as they are easy to replace and seem to go out at the worst times.

We recommended that our clients use Simple Green as well as part of their periodic maintenance, typically twice a year.
https://www.amazon.com/Concent...ef_=aa_maas&tag=maas

A condensate pump is used when the drain line is below grade, or where you want the drain to go. It is frequently used in a basement where you don’t have a floor drain or in a crawl space where you have to pump the water out.

quote:

Originally posted by 220-9er:

quote:

Running the AC results in condensate, not the furnace.

Water is a byproduct of combustion.
Maybe not as much as A/C condensation but it is there and also is acidic/corrosive.

You're right. High-efficiency furnaces don't carry their combustion condensate up the flue like lower-efficiency furnaces do. Forgot about that.

We get lots of water from our A/C in the attic. A pan collects the water and it drains out a pvc pipe routed across the attic and down through a wall to an outside discharge pipe. A/C guy said bleach was bad for the pan. Periodically I hook up the shop vac to the outlet located outside and pull out the slime formed in the pipe.

Wish there were something I could use to stop the build up of slime or mold.

quote:

Originally posted by maxdog:
We get lots of water from our A/C in the attic. A pan collects the water and it drains out a pvc pipe routed across the attic and down through a wall to an outside discharge pipe. A/C guy said bleach was bad for the pan. Periodically I hook up the shop vac to the outlet located outside and pull out the slime formed in the pipe.

Wish there were something I could use to stop the build up of slime or mold.

Hopefully you’re not talking about the pan that’s outside and under the unit.
That’s there in case the drain inside gets clogged or if there is some other issue.

Vinegar is good for mold and slimy biofilms.

quote:

Originally posted by frayedends:
Vinegar is good for mold and slimy biofilms.

White distilled vinegar is the least expensive and very effective. Been using it for this purpose for 20 years.

I just pour some bleach in every few months. Then I dump a few solo cups worth of water to rinse it out.

quote:

Originally posted by ensigmatic:
"Condensate pump?" I'm confused. Running the AC results in condensate, not the furnace. And, I don't know about yours, but ours has no pump. The condensate drops to a pan under the evaporator in the furnace plenum, drains out the back, and into a drain pipe.

Are you perhaps talking about a whole-house humidifier reservoir float switch?

Our condensate drain line also serves the humidifier. Every year, when I change the humidifier evaporator pad, I plug the end of the condensate drain line, fill the line with a 50/50 mix of vinegar and hot water, let it sit for five minutes, then pull the plug.

Our humidifier has no reservoir or float switch. Water runs continuously over the pad during the furnace's heating cycle, with the excess draining out the bottom, into the drain line.

If you don't have a drain nearby, there are small pumps that will pump the AC/Furnace condensate to where it needs to go (sewer line overhead, or to a drain far away for example). They have a reservoir (~1-2qt) to keep from constantly cycling. As long as they can pump down, I don't find I need anything added to keep gunk from growing. But if the discharge line gets kinked & it backs up, look out.

I use 1 1/2 - 2 cups of vinegar every other month during the hot months and once during the cooler months (I'm in Florida). Works very well, and I think it's easier on the equipment than chlorine.

^^I do the same

White vinegar
Cheap

Yep. I use a cup or so of either white vinegar or bleach in the HVAC unit's PVC drain pipe. Whichever is handy.

But I've never found the need to do it monthly or bi-monthly, despite living in a hot and humid area of the South.

Instead, I do it twice a year (usually like April/May and August/September), and have never had issues with buildup.