Can I Replace a Faulty Thermal Expansion Tank on My Hot Water Heating System?

Thermal expansion tanks are imperative to the proper operation of any closed loop hot water heating system. When the boiler heats the water, thermal expansion occurs and the water expands as it’s heated and takes up more space.

Being a liquid, water is very hard to compress. When the temperature rises within the system. so does the pressure within the boiler and the piping. This pressure rise is a natural occurrence and if left unaddressed, will eventually make the pressure relief valve go off, when the system reaches thirty pounds or so.

To absorb this thermal expansion, we add what is known as an expansion tank. This tank is about the size of a propane gas bottle from a barbecue grill for most systems of normal size.

The tank has a tapped fitting on one end and this fitting ties into the boiler manifold somewhere, to connect it to the piping system. A rubber diaphragm, which is installed in the center of the tank, seals off the other side which is pre-charged with a set amount of air.

Air, as apposed to liquid, is easily compressed and this is what happens as the water is heated. The air inside the lower half of the tank is pushed upon by the stretching rubber diaphragm. This air compresses, to allow room for the expanded water to fit without raising the pressure within the system.

This equipment keeps the entire heating system at a preset pressure throughout the heating cycle, regardless, of the system temperature. Without a thermal expansion tank this would be impossible.

Tools To Change Your Thermal Expansion Tank

Most thermal expansion tanks can be removed with nothing more then a properly sized pair of plumbers channel locks. or a properly sized open ended wrench. They simply wind out, unscrewing from the fitting they are attached to. You do however need to do a few things before you remove the old tank.

Check below the tank for electrical system components that could be damaged if they get wet. This would include the electrical service switch and any relays or controls. Cover these items with plastic or something that will deflect the water to a bucket, or some other safe termination point.

Shut off the power to your system and allow the boiler to cool completely. Next, locate the water supply that feeds your boiler. Shut this main intake line and try to isolate the expansion tank, from as much of the system as possible. This would include looking for the two closest valves, that can be shut off to isolate your tank and closing them.

Next look for any automatic air vents that are installed in the piping you have isolated to work on. If there is a vent, depress the Schrader valve, which looks like a car tire stem and relieve the pressure within the piping. Once there is no more pressure, close the cap.

Using the plumbers pliers or the right sized open end wrench, slowly unwind the tank from it’s fitting. Watch the threads once you have it to hand tight. Unscrew the tank a little at a time until you first see a drip of water. Placing a tote tub under the tank will help to avoid making a mess with the small amount of water that will come out. Let the water dribble out slowly until it stops.

Once the line is under a vacuum,(water has stopped draining) the tank can be unscrewed the rest of the way using caution because the tank is usually hung vertically and it will be full of water and weigh about 50 pounds. Two people are recommended for this part of the job, one to slowly finish unscrewing the tank and one to catch it when it lets go.

Installing Your New Thermal Expansion Tank

Match the tank your replacing, with a tank of similar size or larger. Never reduce the size, as this will cause an insufficient amount of room for the thermal expansion your system will create. A normal heating system will usually have a thirty pound thermal expansion tank.

Use Teflon tape, as well as a good pipe sealant compound after the tape. Make sure the female threads where you took the old tank out, are clear and free of any rust or debris. Carefully start the new tank threads into the fitting, paying special attention to not cross thread the fittings, as this happens quite often and easily.

Once the tank is started it can be wound in tight with the plumbers pliers. Make sure the tank is as tight as you can get it and never turn the tank by holding it. Always use a wrench or pliers on the top nut.

After your new tank is installed you can open the water feed to the boiler and the auto vent caps. Next open any valves you closed for isolation purposes and turn the power back on to your heating system.

Always allow your heating system to come up to temperature and shut off on high limit, to be sure you have no leaks. Leaks can occur at one temperatures and not another.

Remember, your hot water heating system, is only as good as the maintenance regiment you provide for it. Leaks cause more leaks and they never get smaller. If you find yourself wondering, Can I Replace A Faulty Thermal Expansion Tank On My Hot Water Heating System? The answer is yes, providing you first gain a little insight, into the operational functions of this equipment. Hopefully this article has helped you to accomplish that.