A Complete Guide to Header Tanks / F&E Tanks

header tank guide

Cold water storage tanks, which are often found in loft spaces, are commonly known as Header Tanks, or Feed & Expansion Tanks (abbreviated to F&E Tanks). The terminology may vary within the industry, but for the purposes of this article, we will use the term “Header Tanks” for any tank which is part of a non-potable/primary central heating system, and “F&E Tanks” for any tank which is part of a potable/secondary hot water system.

Header / F&E Tanks are an integral component within all vented systems, as they serve multiple functions within them. In this article, we will explore those functions as well as several other insights which we hope you will find informative.

Properties built more recently tend not to have Header / F&E Tanks installed, as they are usually fitted with unvented hot water cylinders and pressurised heating systems, neither of which require them. Conversely, older and more traditional properties, which were built before unvented/pressurised systems were invented, more commonly have vented systems (and therefore Header / F&E Tanks) installed.


Contents Overview

What functions do Header / F&E Tanks serve?
Where are Header / F&E Tanks usually positioned?
What materials are Header / F&E Tanks available in?
What other features do Header / F&E Tanks have?
What is the difference between a Header Tank and a Combi Cylinder?
Why you should Isolate a Header or Feed & Expansion Tank
Reasons for Header Tank Overflowing
Overflowing Header Tank – 3 Quick Fixes

What functions do Header / F&E Tanks serve?

Within vented systems, they are how cold water initially fills the system (via a float valve). They also ensure that the system stays automatically topped up in the event of any leaks or gradual evaporation.

A Header / F&E Tank spends the majority of its time accommodating the additional volume that results from the expansion of the system water as it’s heated. In the case of F&E Tanks, which supply cold water to the bottom of a cylinder, they also facilitate and drive the flow of water when the hot taps are opened.

Another minor function is that they both catch any water that may be forced up and out of the vent pipe.

Where are Header / F&E Tanks usually positioned?

As the water level will be the same throughout a vented system, Header / F&E Tanks should always be positioned at a high point within the property, or at least above the highest outlet or radiator. If they’re positioned below a part of the system which they service, that part of the system will not fill and will therefore not operate.

Another important factor to consider is that the higher a F&E tank is positioned, the higher the pressure (and, therefore, flow rate) at the points of use will be. For every metre above the point of use, the weight of the water generates the equivalent of 0.1 bar of pressure, so if you have a poor flow rate at a tap or shower, one option could be to have the F&E tank raised a bit higher.

What materials are Header / F&E Tanks available in?

Most commonly, cold water storage tanks are made from relatively durable polyethene plastic. This is perfectly suitable for vented systems which have temperature-controllable heat sources, such as gas or oil boilers. However, if exposed to excessive temperatures that can be generated by uncontrollable heat sources (like most wood burners), they can be susceptible to damage. The repeated heating and cooling of the plastic can cause it to soften, weaken, and split, in the long term.

As a solution to the above, we manufacture Header / F&E Tanks from copper or stainless steel.

Both copper and stainless steel have their advantages for hot water cylinder manufacturing, but not all of those factors are quite as relevant when it comes to Header / F&E Tanks. Here are the ones that are:

  • Copper has been renowned for its excellent antibacterial and antimicrobial properties for centuries, so for F&E Tanks which supply potable/ secondary water to a cylinder which is heated by an uncontrollable heat source, then a copper header tank would be best. Stainless steel tanks are still perfectly suitable for potable systems, they just don’t have that extra superpower that copper has.

  • If your tank is intended to hold and supply non-potable/ primary water to a heating system which uses an uncontrollable heat source, then a stainless steel version would be just as suitable and would usually be slightly more cost-effective. Our stainless steel products usually have a longer lead time though, so if time is of the essence, paying a few pounds more for a copper unit would be advised.

  • If you need to get your tank into a tight or unusual space which requires a bespoke design, then copper is more flexible for us to work with and would usually be more cost-effective.

  • If you don’t have a well-insulated loft space (and don’t plan to get it well-insulated) then stainless steel is less heat conductive so it will retain heat more effectively.

  • With melting points over 1000°C, both materials are easily able to cope with as much heat as a domestic heat source can produce, over long periods of time.

What other features do Header / F&E Tanks have?

To support their main functions, Header / F&E Tanks have other features:

• A float valve connected to the main water supply

• A low-level outlet which carries water down to the system via the cold feed pipe

• A connection for an overflow pipe to avoid water damage to the property in the event of overfilling.

• An entry point for the vent pipe (usually in the lid).

• A layer of foam insulation to prevent heat loss when the system is is use, and to protect against frost when it’s not

What is the difference between an F&E Tank and a Combi Cylinder?

There’s very little difference in functionality, but there’s a big difference in the positioning of the F&E Tank.

As we’ve mentioned, a conventional F&E Tank is located separately from the hot water cylinder that it serves, whereas a combi (or combination) cylinder has its F&E Tank built onto the top of it. These cylinders are more suitable for properties which lack sufficient loft space, but due to them not achieving the same height advantage that a separate tank does, combis don’t provide as good flow at the taps and showers.

Combi example drawing
An example of a Combi Cylinder demonstrates how the upper section is the system’s F&E Tank.

Why you should insulate a Header / F&E Tank

Even though Header / F&E tanks are designed to store cold water, their positioning in higher locations such as loft spaces, means they are potentially susceptible to particularly cold temperatures. To help protect the header or feed & expansion tank, a layer of foam insulation will prevent heat loss when the system is is use, and protect against frost when it’s not, helping to maintain some efficiency and prevent damage.

Reasons for Header / F&E Tanks Overflowing

There aren’t many realistic ways to pro-actively prevent the over-filling of Header / F&E Tanks, so here are a few causes that you could check for, if/when you notice water coming from the overflow pipe:

  • If your system is new, it may be that the float valve has simply not been set correctly. What is considered to be the “correct” setting may vary, but our advice is an 80mm cold water level for Header Tanks (non-potable water) and a 200mm cold water level for F&E Tanks (potable water).

  • Limescale or other debris could be preventing the rubber washer from making a water-tight seal. Most float valves can be dismantled, checked and cleaned out, so you may consider doing this before replacing the whole valve. If this becomes a regular issue, you may want to consider fitting a strainer and/or water softener on the cold water supply before the float valve.

  • The float valve’s rubber washer will, of course, deteriorate over time. Any pinhole or split in it will inhibit the valve’s ability to stop the flow of water into the tank. In this case, it would probably be best to replace the whole valve.

  • The float may have developed a hole, leading it to fill with water. This will result in it not floating and therefore not providing enough leverage to close the valve. Copper floats are available from us and are, of course, much more durable than plastic ones.

  • If you have confirmed that excess water is not getting into the tank via the float valve, it must be getting in at a lower point in the system. In rare cases, high-pressure water can find its way into a vented system via a defect/leak in a barrier between high and low-pressure parts of your system, such as a coil/ heat exchanger, or a mixer tap. This would backfill the header tank and cause it to overflow. In this case, you may want to employ a Plumber/Heating Engineer to help identify whether this is the cause and determine how to rectify it.


Header / F&E Tanks are critical components of vented heating and hot water systems. With the information and guidance above, you should have a good idea of the roles they play, what can go wrong with them, and how you may be able to rectify any faults that develop with them.

Whenever it becomes necessary to replace your existing Header / F&E Tank, Newark Cylinders can manufacture copper and stainless steel tanks to your specifications. Additionally, our Tanks include a float valve, compression connections, a fitted lid, and 20mm foam insulation.

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