Did you know that not all expansion vessels are the same? Some live inside your cylinder and some sit on the outside. Knowing the difference helps you buy the right part, plan your installation, and avoid any nasty surprises down the line. Let's break it down together
What is an Internal Expansion Vessel?
An internal expansion vessel is built straight into the cylinder at the factory. it handles pressure from the inside without you needing to fit anything extra. You will find these in unvented cylinders like the Megaflo.
The big benefit here is a clean and tidy install. There are no extra components on show, which makes it a great option when space is tight or when you want a clean finish. Because everything is self contained, there is less pipework to worry about too.
The trade off is accessibility. If the internal vessel ever fails, a Gas Safe engineer will need to get inside the cylinder to repair or replace it. This makes the job a little more involved compared to the external fix. That said, with proper servicing , internal vessels last well and rarely cause problems.
What is an External Expansion Vessel?
An external expansion vessel connects to your system on the outside via pipework. You will find these on boilers, sealed heating systms, and unvented cylinders that do not come with a vessel already built in. They are a popular choice for new installation where flexibility matters.
One of the biggest advantages is how easy they are to work with. Engineers can inspect, re-pressurise, or swap out an external expansion vessel without touching the cylinder itself. This makes routine maintenance much quicker and keeps service costs down over time.
External vessels also give you more sizing flexibility. If your system demands a larger vessel, you can fit one without being limited by what fits inside a cylinder. This is especially useful on bigger properties or systems with higher hot water demands.
What Type Does Your Cylinder Need?
Unvented cylinders like the Megaflo, Joule Cyclone and Gledhill Stainless Platinum typicaly comes with internal expansion vessels already fitted. Open vented cylinders and sealed heating systems will need an external vessel added seperately. Always check your cylinder manual or product spec sheet to confirm. It only takes a minute and makes sure you order exactly the right part.
Need a replacement or planning a new install? EDD stocks a great range of internal and external expansion vessels to suit all system types. Shop online today, enjoy £4.50 delivery, and get the right part and the right price!
