Proper Procedure for Bleeding Air from Split Mono-Flow?

zooba72

Hi - I have a split mono-flow system and air gets trapped and needs to be bled out of the system. I've bled air from each of the convectors in the house, but the back side of the house was still not as warm as the front. So I started bleeding air directly from the valve near the circulator on the zone. I have a few questions: I assume this needs to be done while the circulator is running? Should I also close the valve to that feeds the front part of the mono-flow loop while bleeding the back? Final question, do I stop when I no longer hear any hissing from the air seperator? Reason for the final question it was hissing for a really long time and i drained a ton of water. Thank you

Oil Heat Beduerus G215 | Riello Burner | Grunfos Circulators

Ironman

A monoflo is by far the most difficult to purge.

1. Leave the circ OFF.
2. Isolate the loops.
3. Set the fill valve to 25psi until purging is complete.
4. Try adding about 1/8 to 1/4 cup of Dawn dish soap to the system. It will aid in getting air moving.
5. Pray.

R Mannino

I usually start with number 5 and then do 1 through 4.

icesailor

I've always done "None of the above". Once the radiators are vented, the water should be running around the main. If there is no air left in the emitters, and the water is running around the main, it is working. If there is one or two radiators not working, the others are, and the supply and returns are working on those radiators. Something is causing a problem on the ones not working.

The first time I ever heard about putting dishwasher detergent in a heating system was here on The Wall a few years ago. Detergents are corrosive. If they are stand up cast iron radiators, coin vents always worked. Even when 1/2 full of air, they worked unless they were fed at the top of an end. If they are flat fin tube convectors in a cabinet, the old dead guys around where I worked always used those Taco auto coin vents.

On old Monoflow systems, the old dead guys always split the mains into two, like IBR told you to do. They put two balancing cocks at the end of the return above the circulator IN THE RETURN so that you could apply equal flow pressure to both sides. The dead guys thought that you should get the same temperature water at the balancing cocks at the same time.

If it has balancing cocks, DON'T TOUOCH THEM!!! If it is old, and had a B&G Series 100 3 piece circulator and it was swapped for a Taco 007, the circulator may be undersized. I've never seen one that didn't work. According to what I read, they never work. Change it to a 3 speed circulator and try it on high speed. Or whatever speed works.

The only Monoflow system I ever found had a radiator that for years, hadn't worked. When I turned on the water and had the boiler running, it was hot. They complained that it was cold. The radiators that didn't get hot all were caused by the stop on the valve being rusted away on the 1/4 turn stop valves. I fixed them. Still one didn't work. One day, after a very careful hunt for the problem, I discovered that neither leg of this second floor radiator was connected to a Monoflow Tee. Installed in 1964.

zooba72

I'm not an expert, so bear with me here. The original system had B&G 100 circs. I'm not sure if there were balancing cocks at the return, what would that have looked like? There were two gate valves on each of the monoflow returns that I just had replaced with 1" ball valves. The gate valves were very old and I was concerned they would fail. When I had this system updated, the circulators were replaced with Grundfos UPS15-58FRC. I always have heat, but the problem is it's inconsistent between the front and back of house and each convector. I did bleed out the convectors in the summer, but need to do that again. I also believe that I need to close the ball valve on one of the returns and drain water until that pipe gets warm and then do the same for the other side. I had it working well last year but it took me a while to figure it out. Thanks for the response. I appreciate it !

icesailor

Is that a 3 speed pump? Do you have it on "3" or high speed? You replaced a B+G Series 100. That's a different pump. Grundfoss makes so many pumps that it makes some minds swim in confusion as to which pump replaces what.

If it worked before you changed the pump, and doesn't after you changed the pump, it must be something about the pump. It sounds like the flow is too low. If you close one ball valve, and it sort of starts working, the flow is too low. With Mono-Flow systems, unless someone changed something, the mains ALWAYS worked. Its the emitters that had the problem. If you turn on the system and the circulator isn't ripping the water around the mains and back, I'd be looking at something else besides the venting on the emitters.

Crank the pressure to 18-20# and see what happens.

zooba72

Sorry for the late responses, email notifications were going to spam. It is a 3 speed pump and it is working. I actually had it working great last year, I just need to get all of the air out of the system and I forget how i did it last year. I think I shut the front loop off and bled out the air until the return pipe was really hot then closed the front and did the same with the back. I'll play around with now that it's getting cold. Thanks for the responses.