Trouble refilling system after new expansion tank

[mathfogie]

I have what I think is a fairly typical forced hot water heating system. There is a pump on each of the three zone return pipes, before they merge and return the water to be reheated. The refill water goes through a nobackflow valve and into the merged return pipe. The expansion tank and air vent are mounted to an air purger about 6 or 8 pipe feet from where the pipe leaves the boiler. I noticed a large wet spot near the boiler. Looking closer I saw water dripping from the expansion tank. Then I saw the insulation around the hot pipe was wet and finally I saw the air vent was wet and scaly and the top of the tank was rusty. I probably never looked at the tank since moving in, in 1978, but I think the wet spot was no more than 4 or 5 weeks old. I turned off the automatic refill line and drained the system using the three ports on the return lines. It was a pain to remove the air vent and expansion tank because of rust, but time and light oil helped. I replaced the expansion tank and air vent . The real trouble came when I tried to refill the system. I ran a hose from one of the drain ports to a floor drain, opened the valve to that hose and opened the valve on the automatic refill line. Nothing came out of the hose. Same result on all three zones. Same result with thermostats off or on and calling for heat. No lack of pressure at any sink in the house. This smells like I'm doing something really dumb ( not doing something really obvious). I'll gladly admit it it if I knew what it was. Thanks for any suggestions.

 

[Dana]

Some pictures of all of the valving near the boiler and the zone manifolds might make debugging this a bit easier.

Did you pre-charge the new expansion tank correctly before trying to fill the system?

Most systems have ball valves for isolating zones, so that you don't have to drain the entire system to work on it. If you closed the ball valve on one side and drained the system it won't fill (and the system won't work) unless you open it up again.

If there are any screwed fittings or bleeder valves on the baseboards or radiators you can crack them open and do the initial fill without the drain port open, and only crack open the drain port to flush any large remaining bubbles out.

 

[Sponsor]

 

[mathfogie]

Sorry for the delayed response.

Pictures are at the end of this. I will try to post this with the pictures, but if that fails I'll post the text and try some other way with the pictures.

There are shutoff valves on the supply side of the heating system, beyond the expansion tank. One for each zone. When I started reading about replacing the tank, I saw instructions to drain the system, so I did. I did not stop to think that the reason to drain was to prevent water all over the place and an easier way to prevent it would be to close the valves.

I do not know if the pressure is correct. The new tank is an Amtrol EX30. It supposedly comes precharged to 12 psi. The old tank is an Amtrol model 30. Tapping on it before I removed it indicated the diaphragm was still good. I replaced it because it was so rusty I feared it would spring a leak. A cheap, inaccurate tire gauge gives about the same reading on both tanks. I suspect the pressure is close to correct, but I don't know. I will have to find out and adjust the pressure before the final assembly because I don't have any way to add pressure with the tank in place.

I hope to avoid bleeding the baseboards. That involves moving a lot of furniture.

This picture shows the business end of the heating system.

This shows the three motors and pumps for the three zones. None original, all installed at different times.

This picture shows the three drain ports. the one on the right has a hose attached. The shutoff valves were left open throughout the project. The new tank is shown.

This picture shows the autofill setup. The green handle pointing down is how I shut off the autofill. I do not know why the red knob is present, but that valve is open. I suspect the two green handled valves were added when the third zone was added, but I did not document the configuration before that, so I don't know. The backflow preventer is installed correctly to protect the public water supply. There is a backflow preventer built in to each circulater pump or adjacent to it.


Here is a close up of the new tank and valve.

This last picture shows the branching out to the three zones.

 

[mathfogie]

 

[mathfogie]

I can take extra pictures in case any would be useful. Just say what would help..

 

[mathfogie]

Never mind. Problem solved. For a correctly working system, the autofill supplies zero ounces of water per year. For many other homes it supplies perhaps a few ounces per month. A little web research led me to discover the gadget downstream from the antibackflow was a pressure regulator and the gizmo on top of it activated the fast fill feature. So, the solution is open the drain port and open the fastfill, and let it run until the output is steady. That means there are no air bubbles. Repeat for the other zones.

Thanks to the folks that have helped so many of us, here and on other fine forums. Perhaps this solution will help some other DIYer.