Okay I am running two furnaces, on the boiler. No issues before this week. The first furnace that the intake is fine on temperature but on the return line, continuing on the length of the house and upstairs to the furnace there, is much lower than usual. In the past, the return line from first furnace is only a few degrees cooler. No it is pretty cool by the time it reaches the second furnace. No reason present frigid temps would affect such a short run through the A coil. The furnace doesnt draw in outside air. Water level on boiler is fine. Boiler operating fine too. Edit: also, when first furnace fan is not blowing, the return line tempt rises quickly in temperature. It raises the temperature all the way to the upstairs furnace Only thing I can thing is speed of the water flow is low and when the fan is running, it cools the water too much while in the A coil (plenum?)
Maybe the pump is getting weak and can't flow as many gpm as it used to? Do you have a spec for the pump? Can you take the line apart between the two furnaces and check flow volume? Or anywhere before either furnace to check the raw output of the pump?
Jeffrey Svoboda I had the pump replaced last year, it quickly failed and another was replaced, but yes that is my suspicion. Orherwise something clicked the line byt the pump is likely the issue don’t have an opening to check the flow. It makes sense that is the issue
the tech called and plans to come in the morning. House is doing well with the furnaces. I am keeping the boiler operating as normal, so the heat exchangers are as warm as they can be, and I dont risk freezing lines
Circulators generally fail in a short amount of time due to cavitation. Cavitation is caused by air in the system. Is the circulator pitted on the inside ? Is the circulator on the boiler ? Pictures are worth a thousand words too. More info about what causes cavitation - Net positive suction head - Wikipedia
morningwood I presume you are referring to the pump as the circulator? It was replaced just to check on flow performance and the one attached was only a year or less old. Today the temps were up to low thirties. Only thing I have is one of the feed tubes on the exchanger is cool when the rest of the copper tubes on the end of the exchanger are hot. but- once the fan turns off it becomes hot like the others. I am going to pick up a short hose and continue draining of air. A friend who worked a long time in the business said when they have a building with a large boiler system , that it takes a long time to purge air from the line. Next step will be to replace the first exhanger in case there is calcification in the thing.
I know that folks use the two terms interchangeably but what's on our boilers is technically a circulator. A pump builds pressure ( think of a simple bicycle pump ), a circulator just moves liquid from point A to point B. From what I've read it takes a long time to purge the air on a closed loop system, that's why they have air scoops and "stuff" like that. On an open system the air should be purged out in <15 minutes if the circulator is running on a simple system. On the the other thread I showed a picture of my setup. When I initially turned the circulator on for my system after filling I could see the air bubbles in the strainer. I left things alone for awhile and I came back and all of the bubbles were gone. To me that tells me the air is out of the system. It does sound like you are right the track though and might have found the issue with a plugged HX. Do you run any kind of water treatment ? You might be able to get away with soaking the HX in CLR or something like that. If you have puddle pump you might be able to clean it with vinegar too. I did that recently with my flat plate. Good luck.
I just retired using an OWB after 11 years of use. Does your circulation pump run 24/7? My Taco's ran 24/7, 365, and about 2 years was my normal life expectancy. How big is the heat exchanger on the first furnace? What size line running to/from the exchanger? When you replaced the circulator pump in the past when you were experiencing this same issue, did it resolve the problem? My heat exchanger for my furnace would extract a vast majority of the heat from the water. 185° going in, and you could hold your hand around the exit side of the HX. But man, did that sucker throw heat into the house!! When it gets really cold, that demand on first HX goes up exponentially. My two cents worth, I would have never plumbed two furnaces in sequence. I'd have run a 1 inch line from the manifold to each one. Sounds like your heat exchanger is doing exactly what it's supposed to be doing, extracting heat from the water. That's a good thing! I would suggest returning that cool water to the boiler, not to another exchanger. Also, wouldn't be a bad idea to have a boiler drain valve on the return line at the manifold. Very helpful in gauging water flow at the point of furthest return. You can easily check the flow of each loop this way.
