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Specialists in Electric Hot Water Cylinders

Not Servicing Your Unvented Hot Water Cylinder? You Could Be in for a Premature Replacement

16 Jun 2021

Today’s unvented hot water cylinders are technologically advanced. They benefit from new alloys used to manufacture the cylinder body. Improved component design offers better reliability and operability over time. New materials make gaskets and valves last much longer than ever before.

However, for all that, they are not maintenance-free. In fact, forgoing annual service could mean that you’ll be replacing your entire cylinder prematurely, which is a considerable expense. Why would a lack of maintenance lead to premature replacement, though?

Pressure Vessel/Internal Expansion Bubble Depletion

All unvented cylinders have either an external pressure vessel or an internal expansion bubble. These are designed to allow room for water volume expansion as it heats up. As the water heats up, the air in the expansion bubble/pressure vessel is displaced by hot water, thereby reducing the threat of over-pressure situations.

However, over time, pressure vessels and internal expansion bubbles become depleted through normal use. They can be “topped up” during annual maintenance, but if you’re not having your cylinder serviced, that does not happen. This leads to less room for water to expand, which feeds into the next problem.

A Dramatic Rise in Pressure

With less room to expand, heated water creates a massive spike in pressure within the cylinder. The problem becomes worse and worse each time the cylinder is heated, as well. As the pressure continues to rise, failure cascades throughout the system.

Failure of the Pressure Relief Valve

The pressure relief valve is designed as a safety feature to help prevent over-pressure situations from continuing or worsening. When the cylinder becomes over pressurised, the valve opens, releases pressure, and returns the system to the safe range. However, if the cylinder become over pressurised every time it is heated, the valve will fail.

Cylinder Failure

Today’s unvented hot water cylinders are made from very strong steel and are designed to withstand considerable pressure. However, that does not mean that they are indestructible. If the pressure relief valve fails but does so in the closed position, the pressure can lead to structural damage within the cylinder itself. The only option when that occurs is to replace the entire cylinder.

How to Avoid Premature Replacement

While you can roll the dice that your pressure relief valve will stick in the open position, rather than the closed position, that is a very risky gamble. The only sure way to avoid this situation is to have your unvented cylinder inspected annually. A G3-qualified plumber can provide you with a full inspection, as well as annual maintenance, such as draining hard water build-up, and replenishing your expansion vessel or expansion bubble. Note that unqualified personnel, including non-G3-licensed plumbers, should never attempt to make repairs and valve replacements to unvented cylinders.

Ready to protect your water heater from catastrophic failure? Contact EasyFlow today to schedule a consultation with one of our G3-licensed plumbers and to learn more about our annual maintenance plan and how it benefits you.


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