The tech spend a few hours today. I spike of his many years of working on this model boiler, he left defeated Flow is fine, but he installed a new pump to be sure. installed an air purge valve and drained a little air out. What we know is this... air intake coming into the furnace air return is 67 degrees, and comes from a short distance. Tempt coming out of one of the registers is around 120. Even he agrees the temperature drop at the return line is significantly lower than it should. Keep in mind the return line water is the service line for the other furnace- so the lower temperature makes it a problem. only issue may be that 67 is lower than it should be, and causing a drain on the heat as it passes through the heat exchanger. To keep in mind, the house is staying warm running the standard electric furnaces. and the same problem is happening at the upstairs furnace if the service line temp is at high level- as it passes through the exchanger, it drops significantly lower than normal.. Normally the return line temp is only slightly lower than service line, We all are puzzled. Only option may be to replace or clean the heat exchanger just to see.
If you don't have any kind of temperature gauges before and after the plenum you are just guessing at what the problem is. My two guesses would be either air, or the plenum(s) are plugged. I however doubt both plenums would plug up at the same time. Not unless one plenum being plugged leads to low flow to the other plenum. On an open system you don't need an air purge valve. You should be able to purge all of the air out of the lines when you fill it. Plumb a T into lowest point ( basement preferably ) and use domestic water pressure to push the air out. I've attached a picture of my setup.
Am I missing something here? Air goes in at let's say 185° and exits the exchanger are 67°. Register air is 120°. The exchanger is definitely pulling ALOT of heat out of the water. Flow is good per the tech. I still say per my reply to your first post that individual supply lines should have been run to each furnace. I would have never run them in sequence. The exchanger is doing it's job as intended. If you were going to piggy back, go from a HWH to a furnace, but not furnace to furnace. That's tremendous demand on one supply line. What size is the supply line?
Pyromaniac the supply line I would guess is an inch. Pex. Whatever the required line for boilers is. Situation seems to be remedied.
