Constant drip from overflow pipe

Stelcom66

I have a Buderus R2107. I noticed a couple times over the last few months a spot that seemed to be where some water had released. Today I noticed a good amount of water around the furnace. The overflow pipe was dripping constantly. I have a bucket under there for now.

The only thing different is I'm using it much more often than I have in the last 10 years - it's on during the day since someone is in the house, unlike before. I have a wood stove and would typically just run the furnace on a scheduled setting first thing in the morning and before arriving home on workdays. Heat output seems fine. I'll call the company that services the furnace next week - but I wonder what would cause a constant drip, and what causes any discharge from the pipe?

PC7060

May be a bad expansion tank but hard to tell from description. can you provide some pictures of the boiler from few feet back / different angles?

Stelcom66

Sure, thanks. Sorry the lighting isn't great, and I don't see a way to reduce their size.

rynoheat

It's either building too much pressure, or the pressure release valve has failed.

Watch the pressure gauge during a run and see if it goes over 30 psi. If it leaks then, you know why. Most likely explanation is the expansion tank, either failed or lost its charge. Less likely is a failed pressure reducing valve.

A quick test of the expansion tank is to do a quick press of the expansion tank air valve and see if water shoots out. If so replace the tank.

EdTheHeaterMan

Over time that Extrol expansion tank can loose air pressure. Some uninformed mechanics believe that the tank must be tested each time they do a service call or maintenance by pushing the Schrader valve to see if air comes out. All that does is lets air out and that is not what you want to happen. you want to test it with a tire gauge that is accurate at lower pressures like 10 to 15 PSI. And you only want to test it when the tank has no water pressure on the water side. Another way that air can leave the tank is osmosis thru the bladder membrane. I have heard form an Amtrol/Extrol rep that osmosis thru the bladder can account for as much as 1 PSI pressure drop in one year. If you have had that tank for more than 10 years, you may need to pump some air into the tank with a bicycle pump to get it back up to 12 PSI. That may stop the over pressure on the relief valve.

It is important to see if there is water on the air side of the tank first. you can do that my pressing the Schrader valve and see if only air comes out. if you get water, then the tank is defective and can not be repaired. it must be replaced. if no water comes out, then you have a good membrane and you can try pumping 12 PSI back into the tank, BUT IT MUST BE DONE WITH NO WATER PRESSURE ON THE WATER SIDE OF THE TANK.

If there is water pressure on the tank, then the water pressure will compress the air in the tank to match the water pressure as illustrated in this diagram. that i posted in this comment

https://forum.heatinghelp.com/discussion/comment/1747354#Comment_1747354

Hope this helps

Stelcom66

Yes it does help - thanks or the details and diagrams. Things seem to be pointing toward the expansion tank. The system is about 22 years old, so it could certainly be due for adding air, or to be replaced. This and the other posts are great information for reference. Given the possibilities, I'll be scheduling service on the system.

I do have the furnace cleaned annually, I don't know if the air pressure is in the expansion tank is routinely measured. Sounds like it should be, I will ask.

Stelcom66

The bad pressure relief valve was replaced. The tech explained a couple things. One with the well water that I have - sediment can build up over time causing the valve to stick, I guess open in this case. The furnace was installed in 2002 - it wasn't until about 4 years ago that I had a water sediment filter installed. He also asked if I had trouble with low water pressure. I don't - but something I did will cause it intermittently. I have what I believe is a check valve on the well system that intermittently does not close, so the pump will turn on after the holding tank gets below the lower pressure threshold. Since I didn't want the pump running unnecessarily, I installed a switch to disconnect power to the pump if I'll be away from home for a while. I'll sometimes turn it off overnight. Sometimes when returning home or in the morning, there's no water - other times there is, hence the intermittent theory. The furnace tech explained the pressure relief valve senses the low or no pressure and closes as to not allow water from the furnace system into the potable house water. The frequent movement may have aggravated the condition.