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Exploring Hot Water Heater Parts – Buying, Replacing & Installing Tips

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

If you’ve got a hot water heater in your home, you may be wondering how it all works.

On top of that, if you’re looking to install one yourself, or do some DIY fixing of the one you already have, then an understanding of all the parts that make it up will be especially essential. So, what are the parts? And what do they do?

We have the info for you! Below, you’ll find a guide explaining all the different and crucial parts that make up a hot water heater.

Alongside that, there’s information on how to replace and install them. 

What Is A Hot Water Heater?

Let’s start simply, by laying out the basics. A hot water heater is the device that allows you to have hot water through the faucets in your home.

It uses an energy sauce to heat water above the temperature that it’s already running at. 

Gas And Electric Heater Parts

We’re going to be looking at gas and electric heaters, because they are the most common.

Some of the features and parts will be normal, in all the heaters, while others will be added for additional reasons – like improved safety or more efficient heating.

These are parts like hot surface ignitors, powered anode rods, and heats traps. Elements like these make your heater better than it already is, so it’s good to have an idea of how you can improve your device. 

Storage Water Tank

As you can guess, these are for storing water. The storage water tank holds the hot water, and is wrapped with insulations so that the water keeps its temperature

. These insulations are usually made out of polyurethane or fiberglass, and the thicker they are, the better they keep the water’s heat. A good insulation level is 3 inches.

The tanks come in lots of different shapes and sizes, as well as different materials.

Most are made out of carbon steel, however some others differ. For example, a Westinghouse storage tank is made of stainless steel. A Rheem Marathon, meanwhile, is made of plastic.

These other materials don’t need as much upkeep, because they’re better protected from corrosion by the water.

Metal tanks, however, need to have a glass or ceramic lining, as well as anode rods added, to make up for how the water can corrode their materials. 

Heating Elements

These are going to be essential to getting your heat! These are the source of the heat, and you’re going to want something effective and reliable.

Small hot water heater (see also ‘Can A Hot Water Heater Last 20 Years?’) units usually only have one heater element, because there’s less to heat, but bigger ones can have more. The elements themselves are often located at the top or bottom of tall heaters.

If the element is suddenly exposed to air, many have a “dry-fire” feature that will prevent it from getting damaged or going wrong. 

Other heating units have them too. For example, a solar style heating system will have one, as do backup heating units – like a heat pump. 

Gas Valve

The main purpose of these is to control the delivery of the gas to the main burner and pilot light (pilot lights ignite burners). Which gas is being delivered depends, but you’ll either have propane gas or natural.

On top of that, the valve is a safety device too, helping protect the heater and yourself. You know your thermostat? That’s technically part of this valve, because you can make the water hotter and colder through it. 

Gas valves have lots of elements that make them up, and these remain the same across most popular models – like the Robertshaw and the Honeywell.

These features include things like a temperature dial (thermostat mentioned earlier) and a safety limit to control just how hot the water can go – stopping you from getting burned!

Some more expensive models will let you control the temperature to more precise degrees. On top of all that, typical gas valves also have reset buttons and knobs to control the gas.

Anode Rod 

Also referred to as sacrificial anodes, these protect the metal tank from being corroded. We mentioned them earlier!

They work alongside the ceramic or glass lining, making sure that the heated water doesn’t corrode the storage tank over time.

The anode rod is often made of materials like magnesium, zinc, or aluminum. They are located on the top of the heater unit, which means that they can easily be reached if they need fixing or changing. 

More expensive heater units will have powered units that stick around, but anode rods themselves sacrifice themselves.

That’s why they have their other name! They destroy themselves in order to help extend the storage tank’s life even further. 

Dip Tube

These tubes are included in order to bring cold water inside the storage tank. The cold water comes in through the bottom of the tank, with about 6 inches of clearance, while the hot water already has a habit of rising up to the top.

As a result, the water inside the storage tank circulates without any hassle, and this helps to stop scale and sediment from building up and causing problems. 

There are a few different types of tube that are used, which are chosen by the makers of the heater units.

Bradford White, as an example, use perforated tubes because they make a turbulent flow and allow for the most hot water to be produced possible.

PEX (see also ‘Should PEX Piping Be Insulated?’) polymer is often used to make the dip tube, a material which has long lasting strength, as well as brilliant resistance to heat.

Venting And Flue Pipes

The heater unit needs a venting system! They are crucial because they use their flue baffle and pipes to vent out the products of combustion that have been made.

Some of the more expensive models go even further, too, bringing new fresh air in to aid the gas combustion. 

There are a handful of different types of venting systems that you can buy. Some will need new materials for their added features, like PVC or stainless steel. The types include:

  • Atmospheric
  • Direct
  • Power
  • Power Direct
  • One-pipe or Two-pipe atmospheric (with draft hood)
  • Two-pipe Combustion
  • Concentric 

Let’s have a closer look at some and their qualities! The two-pipe combustion vent system gets fresh air from outside the home, getting rid of issues created by homes that have poor inside ventilation.

The concentric system, on the other hand, has a pipe inside another pipe. The larger of the two pipes gets air in, while the smaller inside pipe gets gasses out.

This system can be used with the electric powered blower, or not, it’s up to you! And what is a blower…


These help to push the excess and exhaust heat out to the outside atmosphere, well clear of the heater unit. They are often located at the top of the unit, where they can more easily get rid of the heat.

Each uses a 110/120 volt system, rating about 3 amps or fewer. 

The Gas Burner Assembly

We don’t mean a guide to assembling your gas boiler, no, we mean the “gas burner assembly” – a crucial part of your unit. This assembly has lots of different parts to it. 

The Main Burner

The main burner is where the heat comes from for gas water heaters. The more expensive heater units will have more eco friendly burners, which is important because they are capable of cutting down on Nox emissions.

This refers to Nitrogen Oxides, which are poisonous gasses. The main burner is often located at the bottom of the storage tank. 

Manifold Tube

These consist of a pilot tube, the orifice, and the pilot burner and pilot light. If your heater unit has a pilot light, the pilot burner remains on once the whole thing is manually lit.

Manifold tubes help to ignite the gas, using things like a hot surface or a piezoelectric (which generates electric charge) to do so. 


This is the name for the hole that is drilled in the orifice plug, where gas can escape from all the piping, before going into the burner.

A burner orifice should be replaced if you choose to convert your heater from natural to LP gas (which is liquefied petroleum gas). 


This is an essential piece of safety that will keep your heater in healthy, working condition.

The thermocouple sends the signal from the pilot light to the gas control valve, making a small electrical current that will tell you if the flame is there. This all helps to control the gas delivery. 


These won’t always be there, but might. They’re basically a collection of thermocouples.

They are connected in series, and all continue to convert heat into electrical energy, though with much more efficiency and speed than when you have just one thermocouple. 

The Energy Cut Off

Your hot water heater has many different parts that make it work. If you’re looking to upgrade or change your heater, find out about all their parts here!

Also known as the ECO, this is a metal temperature probe tube that limits the maximum temperature you can have your water heated too.

This will stop you from getting burned by scalding hot water, or damaging the heater. It is usually located on the back of the gas valve, and is put in the water tank. 

The Thermal Cut Off Switch

Also known as the TCO, this is another important control element for you. If the temperature of the products of combustion going on get too high, this kicks in and switches off the gas supply. 

Air Pressure Switch

This works with the electric powered blower in venting the products of combustion that are being made.

These switches are used for all power direct vent heaters and all power vent heaters, used to check that the conditions for good operation are going on. 


You’ll have used one of these in your own home! They are used to change the temperature, and are often mechanical dials.

On top of the thermal cut off switch mentioned earlier, they also help to stop boiling hot water, by being factory set to 120 degrees fahrenheit. 

FVIR And Flame Arrestor

This is very important, helping with any unintentional or accidental ignitions by blocking the flame from getting out of the gas combustion chamber.

FVIR stands for Flammable Vapor Ignition Resistant, which is the special technology it has that helps the arrestor do its job.

More specifically? It’s made of special fireproof material, which is important when dealing with unwanted flames, such as ceramic or stainless steel. 

Drain Valve

These are made to help draining, flushing, and maintenance in your heater. They are usually made of plastic or brass, but they are not equal.

Brass is the much better material to have your valve made from, because they will last longer. Plastic, on the other hand, breaks easily. 

TPR Valve

Also known as the temperature and pressure relief valve, this stops your unit from letting its water get too hot, as well as keeping the water pressure at a sensible level.

That’s right, it’s a little like the TCO and the thermostat! There should be one with every heater unit, and these valves are often combined with the discharge pipe so they go to a good enough drain.


We mentioned this early on in the article, and it is an essential part of keeping your water at a good level of heat.

The insulation is usually given by either fiberglass or polyurethane foam, and both of these are good and efficient at keeping the water heated at the level of heat that you want and need – they don’t let it cool off and get cold. 2 or 3 inches of insulation are usually provided by the manufacturers. 

If you have a cheaper heater unit that doesn’t have very good insulation, you may want to buy an insulation blanket to help up the amount of insulation going on with your water when it’s in the tank.

What’s an insulation blanket? Well, it’s exactly what you think! Like we might wrap a blanket around us when we’re cold, this is a big blanket/cover that goes around your heater unit, allowing it to keep the heat in the water much better. 

Mixing Valves

This is to do with the earlier bits about water getting too hot – this stops it further. Basically, they mix hot and cold water in order to get a water that is a temperature that won’t burn you when you use it.

This means that whether you’re showering or washing your hands, you won’t get burned, rather you’ll just get to enjoy water that is somewhere between warm and hot. It mixes the hot and cold in the branch water line. 

Electric Water Heater Timer

You can guess exactly what these are – and what they do! Timers for your water heater units are included so that the water heating process can turn off during moments when you’re not using the water.

On the reverse, it can turn the heating on when it’s needed. 

The benefits of having the heater is that it’ll lower the amount of energy that is being used up by your heater unit, avoiding waste of energy whenever you’re not using water.

On top of being better for the environment, it will also save you a lot of money, meaning that you’ll only be paying for the amount of energy that you’re actually using – paying bills just for the water that you use, because it’s heated only when you need it. 

Recirculating Pumps

These are very useful if you find yourself waiting quite a while for your water to heat up. We’ve all had this, where there are certain rooms in our house where you’re left with cold water, waiting for it to get hotter.

This can be frustrating if you’re doing washing up especially! If you install one of these pumps, then you’ll get a constant flow of hot water whenever you need it. 

Pumps vary. Some will have a loop from the heater to the faucet, and back, meaning that no water will be left in the pipe.

Meanwhile, you can also get more expensive pumps that have sensors and timers, meaning you can control them more easily.

Additionally, some systems will use an existing cold water pipe to send any unused water back to your heater.

Expansion Tanks

These safety tanks are used to help protect your heater system from excess water volume when the water is being heated, as well as when you have high pressure going on. 

Ordering Repair Parts

Now that you know all the parts, you’ll know which ones you want to order!

When buying them, make sure you have the part number and name, as well as the serial number and model of your heater system. 

However, you shouldn’t always do the repair yourself. If your heater has been exposed to too much moisture, then contact a professional for help. Additionally, if your heater has been flooded, replace the entire thing. 


There you have it! There are many parts that make up a water heater, but this guide should have given a good understanding of what they are and what they all do.

If you need help buying or installing any of them, remember to always ask a professional!

author avatar
Anthony Barnes
Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age


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