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Expansion Tank Problems and Troubleshooting

Expansion tank plumbing pipes crawling up a ceiling

The International Mechanical Code states that every hot water system should have an expansion tank installed within. Most heat systems are designed like a “closed loop" system which prevents the heat from expanding into the air without a mechanical action. In a situation like this, the expansion tank offers enough space for the hot water to expand and contract without the boiler exploding as the system passes from the heating to the resting cycle. However, problems like a leaking pressure valve or low air pressure in the tank can cause expansion tanks to function poorly. While some of these issues can be easily dealt with on your own, it’s advisable to consult a professional when you are unsure of what is causing the problem.

Listed below are a few questions answered by the Experts on issues related to expansion tanks.

I have a 13 year old expansion tank and I find that the pressure release valve is leaking all the time despite having replaced it. I also don’t have any air or water coming out of the valve stem. I have attempted to "charge it" but can't pump air into it. What can I do now?

It seems like your pressure reducing valve is faulty. To begin with, check the water pressure in your home to see if a pressure reducing valve has broken. You can have around 50 - 60 psi but over 80 psi would be a problem. You might have to replace the tank if you can’t check or add air to it.

I need to install an expansion tank on a hot water heater and am wondering if it goes on the cold side or the hot side. My heater is supposed to have a check valve that will prevent the expanded water from going back into the supply line. If this is the way it works, is it possible for the expanded water to go into the tank if it is on the cold side?

Since the pressure would be equal everywhere, you could install the expansion tank anywhere on the system. It is usually installed near the heater on the cold water line. The heat traps or “check valve” you have shouldn’t affect the pressure on any side and will stop the lighter hot water from moving out of the tank.

My expansion tank is located in the crawl space on top of my bedroom. During winter time, I hear the water moving up through the pipes and when it gets warmer, it flows back down to the boiler. What can I do about this?

The expansion tank you have seems to be an old one and should be replaced with a new bladder style one. A bigger pump might help to circulate the water faster but may cost a lot. It’s always better to consult with a hot water specialist before you carry out any of these changes.

My expansion tank is leaking. To prevent water from flowing out of the tank, I switched off the main water valve. Owing to the cold weather, I didn’t shut the boiler off. Could this damage the system?

Case details: My boiler is an oil-fueled one, I have forced hot water baseboard heat and the system is tankless.

It doesn’t look like you have any cause to worry since your boiler should have a water level control safety cut off like all tankless systems.

I installed an expansion tank on the cold inlet side of the hot water heater and find that the pressure relief valve has started leaking. How do I solve this problem?

It seems like you may have to install a new Pressure Reducing Valve. You could try to trip and reset the system but it may not work. It’s better to replace it to solve the problem.

Can I fix a leak in my Watts potable water expansion tank myself or do I need to call in a professional?

Case details: It may be leaking from the threads in the tank since the tank is wet on the outside.

Try shutting off the water and unthreading the tank. Then re-tighten the threads using teflon tape and thread sealant on the threads. If the leak doesn’t stop, you might need to call in a professional since the threads could be rusted or the leak may be from a point that is far more difficult to fix.

There are a few steps to follow to check if your expansion tank is working properly. To start with, tap the tank. If you hear a thud sound in place of a hollow sound, it could indicate a damaged diaphragm. Next, check the temperature by feeling the top and bottom of the tank. If the tank is working alright, it should feel cool on top and warm at the bottom. After this, check the air pressure inside the tank with an air gauge. It should be 12 psi. Finally, examine the release value for any water residue. Presence of water could indicate that the pressure in the tank is too high. To understand more about expansion tanks, turn to an Expert for professional help.

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