Do you have to drain a water heater to replace an expansion tank?

Author: Icie Schulist Sr.  |  Last update: Saturday, March 15, 2025

Whether you're adding a new expansion tank to an existing water heater or you are replacing a water expansion tank, you will need to drain your water heater.

Do you have to drain a water heater to install an expansion tank?

If you already have an existing water heater and you're adding an expansion tank on top of that, then you need to drain the water heater. Before you get started, you will want to make sure there is enough space over your water heater where the expansion tank can reside.

Can I replace my expansion tank myself?

Unless you have a valve that isolates your expansion tank from the system, you'll need to drain the pressure off the system, remove the tank and install a new one, then refill. This process will usually introduce air into the system. How the air is removed largely depends on original system design/installation.

How much does it cost to replace the expansion tank on a water heater?

A water heater expansion tank costs $150 to $450 on average, with a national average of $325. The total cost depends on the size and type of tank. A water heater expansion tank costs an average of $325 to install, and most people pay between $150 and $450 for the task.

Can I change an expansion vessel myself?

Generally, the pressure on your central heating system will be 1.5 to 2 bar. When it is lower than 1.5 bar, it is very likely that the expansion vessel is broken. Replacing an expansion vessel is very simple. You can easily do it yourself, and thereby save the cost of calling in a fitter.

What Is This Tank? How to Replace and Maintain a Water Heater Thermal Expansion Tank

What are the symptoms of a failing expansion vessel?

Firstly, you may observe fluctuating pressure levels within the system, which can manifest as inconsistent water flow in taps or heating systems. Another sign is the frequent activation of the safety pressure relief valve, indicating that the vessel isn't maintaining proper pressure.

What is the rule of thumb for expansion vessels?

The 'rule of thumb' calculation is that the pressure vessel size is equal to 6 seconds of maximum flow. For example: if the design maximum flow rate of a booster set is 3 l/s – the required vessel size would be 18 litres.

How long does it take to replace an expansion tank?

However, most tanks last between 5 and 10 years before needing to be replaced. If you're unsure whether your expansion tank needs to be replaced, it's best to consult a professional plumber.

How can you tell if an expansion tank is bad?

If air comes out, your expansion tank is working. If nothing or water comes out your tank is bad and needs to be replaced. When a hot water expansion tank works correctly, you will probably see no problems with leaks and other issues.

What is the life expectancy of an expansion tank?

However, on average, an expansion tank can last 5 to 10 years or even longer if properly maintained and inspected regularly. It is recommended to check the expansion tank for signs of damage or wear, such as leaks or rust, at least once a year and replace it if necessary.

How do I drain my expansion tank?

First place a bucket beneath the purge valve on the tank, or attach a hose. If nothing comes out, there is the possibility that you have a big of a vapor lock. Be very careful at this point, as the best way to do away with this problem is to blow into the faucet of your expansion tank.

Who fixes expansion tanks?

You must call a plumber immediately if you notice any water leaking from your expansion tank. They will evaluate the issue and ensure it is properly repaired or replaced before further damage occurs.

Do I really need an expansion tank on my water heater?

An expansion tank is required on the supply line coming into the tank to reduce the tank stress which will shorten the tank's useful life. An alternative to the expansion tank is an approved pressure relief valve assembly. These devices are required on closed systems, which is public water.

Is it code to install an expansion tank on a water heater?

Expansion tanks are required by code in all new water heater installations in closed systems. A closed water system uses check valves, backflow prevention devices, pressure-reducing valves, or other devices on the supply line to prevent water from being sucked back into the municipal water supply.

What happens if an expansion tank is full of water?

If the expansion vessel is completely filled with water, it would lose its ability to manage pressure effectively, as there would be no space for the water to expand. This could lead to pressure surges, which may damage the boiler system or compromise its efficiency.

Does a hot water heater need to be drained?

It's generally a good idea to drain your water heater at least once a year, according to both Bob Vila and Family Handyman. If you live in an area with hard water (that has high mineral content), Angi recommends you may want to drain it every six months, or so.

How much does it cost to replace a water heater expansion tank?

The cost of replacing thermal expansion tanks can vary, but usually falls somewhere between $250 and $500.

Should the expansion tank be full or empty?

Your expansion tank should be half full of water and air. Using a metal object, tap the top and bottom half of the tank. The sounds should be quite different, which indicates that your tank is filling up the way it should.

Why do I suddenly need an expansion tank?

When extra pressure builds up in the hot water system, it could cause pipes to burst, resulting in costly repairs and even greater risks if someone gets hurt. With an expansion tank installed, excess pressure is diverted away from pipes and other components which can help prevent accidents and damage.

What happens if you don't install an expansion tank?

As plumbers know, the expansion tank equalizes pressure throughout the plumbing system by providing a space for hot water to flow into. Without an expansion tank, pressure would be distributed to the entire plumbing system, straining it and decreasing its lifespan.

Does an expansion tank need a maintenance?

Drain the tank and ensure that it is free from dirt and foreign debris. Check pre-charged pressure. Over time, air or nitrogen gas can find its way out of a sealed tank. It is important to test if the pre-charged pressure in the tank still matches the calculated pre-charged pressure required.

What happens when a well expansion tank fails?

Potential for Water Damage:

Water damage to the surrounding region may result from a leaky tank or an overused pump that finally breaks. It might damage your house's walls, flooring, and foundation, necessitating costly repairs.

How often should an expansion vessel be serviced?

Check the expansion vessel during annual service

This includes draining the system and ensuring the expansion vessel is working under the correct pressure.

What is the 3 tee rule in plumbing?

Pipeing design dicatates that the last return before the returns feed into the must be the Hot Water. It is known, to the ones in the know, as 'The Three Tee Rule'. Which means that the first 'T' into the return is the Feed, the second 'T' into the return is the heating and the last 'T' the Hot Water.

How do I know what size expansion tank I need?

Choosing the right size for your Expansion Tank

The decision will be based on two factors. The first is your hot water heater's or boiler's capacity in gallons. This information will be on your water heater's or boiler's factory label. The second is the water pressure in your piping system.

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