Expansion Tanks: Signs of Failure, Safety Concerns & Costs to Replace

Expansion Tank Lg

If your house has a water heater, there is a high chance that you have a thermal expansion tank. However, if the expansion tank ceases to work, you might find yourself in a severe problem. 

When such a thing occurs, you must solve the issue immediately. The problem can be severe to the extent that your expansion tank explodes. 

An expansion is meant to handle the thermal expansion of water. If the pressure rises to uncontrollable limits, it can damage joints in supply pipes, valves in plumbing fixtures, and even the water heater. A leaky temperature and pressure relief valve is one sign that your expansion tank has failed.

However, if you regularly work with a professional who does regular inspection and maintenance, you can prevent your tank from being compromised. This article will explore the signs of failure of an expansion tank and the cost of replacing the tank when it fails. 

Top 5 Common Expansion Tank Problems

The good thing about an expansion tank is that it helps to regulate air and water pressure in the water system. The tanks are also easy to maintain. However, they are not immune to developing different complications. These issues are common and don’t require a professional to notice. Let’s look at the top problems you might encounter:

Venting Water

If an expansion tank stays for a long time, it might experience tears and wear in critical areas. It will lead to the tank leaking water. It’s therefore vital that you closely monitor the expansion tank and see where the leak is originating. 

If, by any chance, the leak is from the pipe found at the top of the expansion tank, try tightening the fitting by yourself. Here, you can employ a wrench to do the tightening. However, never over-tighten it. 

However, the best solution is to engage a plumber who can assess the problem well and fix it professionally and determine whether you must replace the tank or repair it.

Air Blockage

An expansion tank is designed as a place where air can stay within your hot water system. Of course, the air is required in any water system. However, air can be trapped and lead to what we refer to as a hydronic airlock.

This airlock can lead to water not flowing through the pipes or heater. If you’ll notice that there is no water in the radiators, there is a high chance that you’re experiencing an airlock.  

The function of an expansion tank is to prevent such an air block from ever happening. However, if you notice that you have an air block, it points to the fact that your expansion tank isn’t functioning normally. 

A plumber would help determine whether the tank needs a fix or an entire replacement. 

Steel Tank Needs Recharging

There are at least two types of hot water heater expansion tanks. The older tanks are developed from steel. Steel tanks usually combine air and water inside to maintain pressure. 

However, with time, the water inside can absorb small quantities of air. When such a case happens, the expansion tank will lose its pressure. 

The solution to this air/water ratio challenge is to ‘recharge’ it. You can call a professional plumber to recharge the tank for you or do it yourself. 

If you want to recharge the tank, you should close the isolation valve, drain water out of the expansion tank, and reopen it for a refill with the perfect quantity of water. 

The challenge with doing it yourself is that you can’t see the inside of the tank. It’s therefore wise to involve a professional. 

Not Having Enough Air in the Diaphragm Tank

The newest version of expansion tanks employs a rubber diaphragm system. The diagram is used to separate air and water. Diaphragm expansion won’t lose any pressure since water will absorb air. 

The most common challenge experienced in a diaphragm tank is losing small quantities of air pressure via the valve. When this occurs, there is a need to add more air into the tank. 

The addition of air into the tank is a straightforward task. All you have to do is pump air into the tank using a bike tire or air compressor pump. Then, the tank has to be filled to 12 PSI.

There is a high chance that the tank will not hold air pressure after filling it with excess water or completing the fix. If this is the case, then you must replace the whole diaphragm. A professional plumber can let you know whether you’ll need to replace the entire diaphragms or it’s just a minor repair. 


Another sign of failure in expansion tanks is condensation happening there. If you spot any buildup in condensation, there is a high chance you need a plumber. 

Condensation in the water tank might cause rust. It might also cause water to drip onto electric wires. Finally, if you don’t address the challenges immediately, the water droplets might cause problems with the flooring under the tank. 

Since the cause of condensation is difficult to determine, we recommend that you seek the attention of a professional plumber when you notice related signs. 

How Backflows Affect Thermal Expansion

The chances of thermal expansion will increase if you add a backflow prevention assembly (check valve) connected to your cold water line. It’s a known fact that water flow is unidirectional, from the supply unit, through the meter, and into the customer tap. 

Although water is set up to flow in one direction, there are cases where it can reverse its flow. If hot water flows in the opposite direction, we call this a backflow. The situation occurs when backpressure or back-siphonage condition is created in the waterline. The backflow preventer helps prevent hot water from exiting the water heater through the cold water pipe.

Backsiphonage involves water moving in the unintended direction via the force of suction created by a vacuum. A vacuum can happen during the shutdown of the distribution system, when a plumbing system breaks down, or when pressure is lost in the system due to a high water withdrawal. If pressure reduces below the atmospheric pressure, a vacuum is created in the piping system that establishes a back-siphonage. 

Backpressure may result from a source pressure, including thermal expansion, creating tremendous pressure than the one supplied from the distribution system. The excess pressure might push water in the opposite direction and backward. 

Avoiding Common Water Heater Expansion Tank Problems

Unfortunately, water heater expansion tanks don’t last for a very long time. You might find the tanks getting waterlogged and thus being unable to function effectively. It’s recommended that you at least replace the tanks after 5 to 10 years. However, there are several things that you must do to keep them in good conditions:

  • Watch out for condensation. Like we have seen above, condensation can result from several causes, including a humid climate or a waterlogged expansion tank. Either way, it can be dangerous, especially if the water heater is near electrical devices.
  • Do a tap test. The test involves knocking and tapping on the expansion and listening to the sound that it makes. If you hear a ringing, hollow sound, know there is still air inside. If the sound is duller, the tank is filled with water and needs a replacement. 
  • Feel the tank. Another important thing that you can do is to feel the top and bottom of your expansion tank. The top of the expansion, which must have compressed air, should have a cool touch. The bottom part of your tank should feel warm. If the bottom and top of the tank feel the same, a problem needs a solution. 
  • Closely monitor the water heater’s pressure release valve. The release valve releases water in case there is a lot of pressure for the tank to handle. If the release valve is constantly dripping, it isn’t functioning correctly, and a replacement is necessary. 
  • It would be best if you upgraded the expansion tank before it completely fails. There is no need to wait for a long time until the problem is beyond repair for you to invest in a new expansion tank. The best practice is to replace the tank every time you change or service the heater. 
  • Replace a faulty tank immediately. Your home is at significant risk if the expansion tank isn’t operating at 100%. Immediately you notice something abnormal, contact a plumber and make necessary arrangements for a new expansion tank. 

Why Put Expansion Tanks on Water Heaters

Even before we focus on why you need expansion tanks on all water heaters, let’s look at the closed plumbing system:

Closed Plumbing Systems

Plumbing systems can either be closed or open. For open systems, water can move in and out of your house through the central supply unit. An increase in water as a result of thermal expansion will force water out of the system naturally. 

However, the same can’t happen in a closed system. Having an open system in homes can have a devastating health risk, thus explaining why most people have a closed system. 

However, where there is a water heater, the volume of water increases. So how can plumbing networks deal with excess volume and pressure resulting from water heaters in closed systems which don’t allow water to leave your home? The solution is the installation of a thermal expansion tank. 

Why Worry About Pressure?

You might be tempted to think that high pressure in your water system isn’t a big deal. However, water pressure is a critical aspect of your water system. 

However, in cases where the water pressure is very high, appliances, pipes, and fixtures are exposed to extra stress. For instance, your faucets, showerheads, and toilets are designed to function under a specific pressure limit. If you exceed that limit, these appliances might break down and consequently need replacement.

Having a high pressure can lead to small leaks that may go unnoticed for months, more so if they are under floors, behind walls, or above ceilings. The small leaks may cause toxic mould growth, rotting of the wood frames in your home, and structural damage. 

Very high pressure can also translate into instant pipe bursts that can cause property loss and catastrophic damage. 

It is therefore essential that you monitor yourself for any high-pressure signs. However, the best solution is to install an expansion tank on water heaters

The Cost of Replacing an Expansion Tank

Replacing a bad expansion tank is something that you should do after five to ten years or immediately after you notice a problem. The cost can vary depending on different factors.

Factors Affecting the Cost of Replacing an Expansion Tank

  • The personal installing the tank – The most significant portion of the cost of installing or replacing an expansion tank is spent on labor. If you can do the replacement yourself, you stand a chance of saving up to 75%. If you involve a professional, it would be best if you choose a cheaper but reputable plumber. 
  • The type of support on the tank– Using a simple plastic strap or metal to support the tank’s weight might cost a few dollars. If you use steel brackets instead, you should be ready to spend 3-5 times the cost of buying the tank. 
  • The cost of the tankThe cost differences between a 2-gallon and a 5-gallon expansion tank are minimal. However, big expansion tanks are more expansion. The quality of the tank also affects its cost. 
  • Installation factors – if your expansion tank can be accessed quickly and there is more room to work, the installation costs may be lower. However, when it is found in a utility or cramped crawlspace, the prices might skyrocket. 

The Cost of Tank Installation Supplies

The size of the expansion tank you require will depend on the incoming water pressure and the water heater capacity. It is especially critical if you own a good pump. Since residential water heaters range between 30-100 gallons, expansion tanks in most cases are less than 5 gallons. 

Here are the costs of expansion tank installation supplies:

  • Expansion tank, 2-5 gallons – $35-$70
  • Steel Tank mounting bracket – $50-$200
  • Metal hanging strap – $6-$12
  • Pipe cutter – $15- $25
  • 10″-14″ pipe wrench – $12-$20
  • One ¾” connector – $3-$8
  • Copper tee – $2
  • Copper pipe short section – $6-$8
  • Teflon pipe tape – $2-$4
  • Copper threaded female union – $4-$8
  • Soldering kit – $25-40

Your best option is hiring a qualified plumber to do the job for you. For most pros, the complete replacement will take 1-2 hours. The labor cost includes:

  • Plumber rates: $75 – $150 per hour
  • Handyman rates: $60 – $100 per hour

How to Replace Your Water Heater Expansion Tank

The replacement process is relatively straightforward. Just go through the steps below to succeed:

  1. Identify the old expansion tank 
  2. Proceed to turn everything off
  3. Drain water from the tank
  4. Disconnect your expansion tank
  5. Attach the new expansion tank and pressurize it
  6. Check the pressure
  7. Apply Teflon tape
  8. You on everything that was initially off

Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.