Service Valve Buying Guide

Service Valve Buying Guide

John, DIYer & IT developer, Brighton

Guide written by:

John, DIYer & IT developer, Brighton

71 guides

Service valves are essential safety components for electric water heaters. Whether they are brass or stainless steel, straight or angled, with or without dielectric connectors, their features are determined by the type of installation and water quality.

Important features

  • Straight
  • Elbow
  • Brass
  • Stainless steel
  • Dielectric connection
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What is a Service Valve?



Service valves are essential components of an electric water heater.  They manage the balance of heat and pressure in a water heater tank and are made up of several parts:

  • A check valve prevents hot water from back flowing into to the cold water entry to prevent water pollution or legionella contamination;
  • A quarter-turn stop valve shutsoff the water supply;
  • A relief valve, calibrated to 101.5 psi, opens in case of too much pressure in the tank. This occurs when the volume of water increases due to its expansion as it is heated or if the temperature in the tank too high;
  • A control knob or thumb switch on the valve for drainage which should be used prior to draining the tank directly.

Service valve: configuration and materials


In all configurations, service valves are connected using a 3/4 "(20 x 21 mm) coupling, the male end for the main and female end for the water heater.



Elbow service valves are mounted on horizontally positioned water heaters where their connections are located on the side.  The elbow valve is attached at the cold water entry of the water heater where it forms an angle between the discharge tube and the cold water intake. The elbow valve can sometimes be adjustable.



This is the more conventional format of the service valves.  The service valve is attached vertically beneath the water heater and is aligned with the discharge tube.The cold water entry is located on the side at a 90 degree angle to the valve. This configuration corresponds to the majority of vertical heaters and some horizontal.




The seat of standard service valves are made of brass and is used in fittings for plumbing.It is less expensive and easy to work with, making it perfect for a device as complex as a service valve.

Stainless steel


Brass quickly shows its limits when water is hard and full of mineral deposits, too acidic, or contains pollutants.The resistance of stainless steel to scale is a clear choice.  Ask a professional about its care and maintenance.

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What are the specifics?

Scale Resistant


If you live in an area where water is hard and your installation is not equipped with a water softener, a scale resistant service valve is the right choice: valve seat made of steel or ceramic is less likely to corrode .


The dimensions of the hardware fittings are 20 x 21 mm or 3/4 ", the male attachment for the cold water entry and the female for the storage tank.


Teflon is a polymer with outstanding non-stick and lubricating properties as seen with cookware. The gasket of a service valve, coated in Teflon, mounts much easier and doesn't clog or corrode.

Integrated dielectric

When different types of metals are joined together in plumbing, they can develop a small electrical charge that can corrode them. Using dielectric unions prevents rust from forming on the water heater tank and are sometimes advised to be used at the cold water intake.As it is already integrated into the service valve, you do not have to worry about it! If you follow other tips, you can find independent fittings that can be mounted on the hot water outlet.

Maximum temperature

The maximum temperature depends on the size specifications of the tank.  It is necessary to refer to the manufacturer’s instructions.

Capacity of the tank 

The service valve can be preset for a recommended specific volume, ie 200 liters etc.


Acceptable maximum pressure of a service valve must be respected for its optimal function.

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More information

To learn more about the different accessories of electric water heaters and the production of hot water, consult the buying guides:

For the maintenance and installation of your electric water heater, consult our installation and maintenance tutorials : 

Find out more about hot water production solutions with our guides : 

  • How to choose your gas water heater?
  • How to choose your thermodynamic water heater?
  • How to choose your solar water heater?

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Guide written by:

John, DIYer & IT developer, Brighton, 71 guides

John, DIYer & IT developer, Brighton

Since I was a child, I was always interested in manual and technical works. Always fascinated by woodworking, I took advantage of my first flat as a playground. On the cards: electricity (of course, safety first!) and some partition walls; but also decorating with the help of the missus, made-to-measure furniture and little tricks to optimise the space, all the while remaining as original as possible. When the little one arrived, I started building bits and pieces for him! Lacking space, I have not got a permanent workshop and certain tools I dream about but are not part of my collection. Not to worry, I already know a lot about DIY and I have a high-tech profile that I hope will guide you in your decisions!

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