Get Servicing Savvy About Cylinders

Annual servicing of cylinders is key to ensuring the safety and efficiency of their operation. George Linder, product manager at Heatrae Sadia, discusses the essential maintenance checks that should always be carried out when servicing an unvented cylinder.

Following Guidelines

It’s important to access and follow the manufacturer’s guidelines, to ensure that the servicing process is specific to the hot water cylinder model, and these can usually be accessed via the manufacturer’s website. All installers must be G3 trained to carry out any cylinder servicing, and this qualification can be gained through the completion of a G3 Unvented Hot Water Storage Cylinder course. Upon successful completion, a G3 Unvented Certificate and an identification card will be provided.

A further benefit to gaining G3 certification is that this opens the door for an installer to join a competent person scheme. This makes it simple to register hot water cylinder installations with building control, which is a legal requirement.

Examining Moving Parts

Checking the key components of a cylinder is an important part of routine maintenance. This should include examining the safety valves to ensure they are allowing water to flow through freely. To evaluate their performance, manually operate the T&P and pressure relief valve for a few seconds, and the water should flow through the tundish and water should discharge freely through the pipework. The valve should then reseat correctly once released.  

While carrying this out, it’s worth exploring if the internal tank needs inspecting too. If so, this can be done through the immersion heater boss.

If an issue is discovered and the immersion heater needs to be removed and replaced, careful attention must be paid to ensure that the tank is not damaged. Using the wrong tools and methods can cause damage to the immersion boss, resulting in potential leaks.

Removing Debris

For Megaflo cylinders, a strainer is present to collect debris, and this should be cleared during checks. In order to clean the strainer, the main stop cock to the system needs to be switched off and following this, the lowest tap in the system can be switched on to relieve any pressure build up, and then a spanner used to unscrew the pressure reducing cartridge to allow the installer to remove the surrounding moulded housing. The strainer is located within this cartridge, so it can then be taken out and held under running water to wash away any particulate matter.

Descaling the Immersion Heater

For those based in hard water areas, descaling the immersion heater is particularly important as it will help to extend the life of the cylinder and boost performance. Ahead of carrying out this work, the mains water supply and boiler must be switched off and the electrical supply should also be isolated.

A hosepipe can then be attached to the drain cock, which will take the water to a suitable discharge point, opening a hot tap will aid the draining of the cylinder. Once the cylinder has been emptied, the covers to the immersion heater can be opened to allow the disconnection of the immersion heater thermostat.

Once these steps have been completed, the immersion heater can be lifted out by simply unscrewing it while handling it carefully so that any scale can be removed. Extra care also needs to be taken to ensure the sealing surfaces are clean and undamaged. If there is any doubt about the seal, a new immersion gasket should be fitted to avoid issues. Finally, the heater can be replaced, while making sure the immersion heater gasket isn’t trapped. Fill the unit, rewire, check, close and secure the housing cover to finish the process. 

Recharging the Expansion Vessel

When needed, the air volume within a cylinder should be recharged to accommodate for expanded water. If water is intermittently flowing from the expansion valve, then this indicates that the air volume may have reduced so much so that it cannot accommodate expansion.

To recharge the heat source to the cylinder must be switched off, as well as the water supply. This can be done by turning the isolating valve. On a Megaflo cylinder, the blue handle needs to be rotated so it is positioned at a 90-degree angle to the flow of the water. Following this, open the lowest hot tap supplied by the cylinder and hold open the temperature and pressure relief valve. This can be done by twisting the knob on top of the valve until the water stops and the gurgling sound at the valve stops.

Now the pressure and temperature relief valve can be closed by releasing the knob, and the isolating valve can be switched on by rotating the blue handle until it runs parallel with the water flow. Once water is flowing from the hot tap again, it can be turned off. The air volume will now be recharged as the cylinder refills. 

Servicing Savvy

While many are aware of the need for an annual service for a boiler, fewer homeowners are aware that this is also required for a hot water cylinder. It is therefore important for installers to share this knowledge with homeowners and discuss the benefits and safety considerations when it comes to regular servicing and maintenance.

For further information on cylinders and commonly asked questions related to servicing, please visit

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