How To Remove Air From A hot Water Heating System, is something every homeowner is going to wish they knew the first time they are sitting down watching TV and the sound of a swift stream runs through the room. The heat will come on and a flush of gurgling water will be pumped into the baseboard or radiators. This noise of water flowing is a sure sign that your hot water heating system has somehow been infiltrated with air in the lines.
There are several different ways that air can get into a hot water heating system and all of them will need to be repaired and then the system will need to be purged to completely alleviate any micro bubbles that are hiding in the piping. These systems run with water being pulled or pumped by a circulator pump and when this pump encounters a slug of air it will get an air lock and lose prime. When this occurs, a heating outage is experienced. We all know that rule of thumb is, it will always happen on the coldest weekend day that happens to fall on a holiday and will cost us our next born to get a service man out there.
One way that air can get into a system of this type is when a thermal exp[asion tank blows it's rubber diaphragm and expels all of the pre charge they come with into the piping. When this happens the tank must be replaced and the system must be repurged to get all of the air out.
If you tap an expansion tank on first the bottom half and then the top half, the sound should be dramatically different. The top half, or the half that is connected to the system as some hang these upside down, will have a solid filled sound. The bottom half of the tank is charged with air and separate from the top, when you tap here it will have a hollow ringing sound. This air when properly functioning, absorbs the thermal expansion from the heating system as the water heats. When the tank is blown the bottom will also sound solid as it will also be flooded with water.
Hot water heating systems run under about 20 pounds of pressure so do not just unscrew the tank. A qualified serviceman should be the one to replace the expansion tank.
If you are attempting to change your own tank then the power to the system, the water feed to the system and all valves available to help isolate the expansion tank from as much of the system as possible. Some tanks when properly installed will have a shutoff that controls only that and this tank is easy to change. Some systems will not be this easy and it may be necessary to pull a vacuum on the system or drain it entirely to perform this service. Either way the system will have to be purged entirely to put it back into service.
Another way that air can get into the system is through a small leak on the suction side of any circulator pump. When the system first comes on or calls. The pump starting up will draw a little gulp of air from the leak. This air over time will collect and form larger bubbles that will stall the flow and inhibit suction of by the circulator pump. Notoriously, circulator flange gaskets have been know to be a source of air getting in. Tighten the bolts on the flanges that hold the circulators in and make sure there are no leaks any where on or near the boiler.
After the reason for the air has been determined then we can repurge the system and restart the flow of heat. Look for a purge setup on your boiler. Some will have one setup and some will have more then one according to how many zones are in the system. All zones must be purged and starting from the farthest one away from the boiler to the closest purge each zone until no air is present.
The purging process is done with city water pressure or a well pump and well water if you are on a well. One other way we may have to purge would be with a recirculation pump if anti freeze is in the system that we don't want to lose.
A hose is connected to the boiler drain in the purge setup. This setup contains a ball valve that will stop feed water from just going right out the hose and instead forcing it around the zone throughout the radiation and back out through the boiler drain pushing all the air as it goes.
A five gallon bucket with the end of the hose in it will show you if there are any air bubbles left submerge the end of the hose in water and just watch it until all the bubbles are gone. Then proceed to the next zone.
After all zones have been purged we are ready to put the system back in operation. This is done by opening any valves we have closed. Place all equipment back into the position they were in before we started. Now turn on the electrical switch and the boiler should fire. Listen to radiation as the heat runs and assure you have gotten all the air out. A nice quiet system will mean you have been successful. If there is still the sound of water running through the pipes then the process must be repeated.
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