Monoflo System will not heat after drained for service.

Mono-flo systems work well as long as ther are no air pockets in either the supply or return pipes to the convectors.This type of system requires the run-out pipes (piping between the main around the basement to the radiation) must always go uphill gradually from basement to convector. The convector element could be cast, copper, or steel pipe. The element should be installed so the element in the cabinet has a vent on the high side which would be the return side piping. This convector is correctly piped.

I have encountered a problem after I drained a system for some type of service which was baffling at first. When the system was refilled all the radiators or convector's heated except maybe one or two even though they all heated prior to the service. This problem is usually due to homes settling through the years and the piping now has a high point. This means there is not a gradual uphill slope from the main piping to the radiation. The high point will trap air and when bleeding you get air than water. Since more bleeding only produces more water you believe the problem is not related to air, but in this situation, it is air related. Bleed all day if you want and you will not get the air out of the pipe with a high spot.

The problem is this

The water will go up the pipe that is not air locked and you believe there is no air, so we want to blame something else.

Having the pump mounted on the supply pumping away from the expansion tank and adding pressure to the system may help in getting this system to work overtime. I have seen it take two weeks and sometime not at all without manually solving the problem.

This is how the Water will flow when purged

Once the radiation and piping are purged it will get rid of the air and the unit will heat fine.

For cabinet convectors and baseboard, the radiation should slope slightly toward the vent side of the radiation so the air can move to the highpoint and get vented out.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, installations should be reviewed on a per job situation. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or it's personnel accepts no responsibility for improper information, application, damage to property or bodily injury from applied information found on this website as it should be reviewed by a professional.