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Specialists in Electric Hot Water Cylinders

Water Heater Leaking: The Most Common Causes

28 November 2023

Unvented cylinders offer outstanding performance and reliability. If you’ve primarily used older-style vented cylinders, the difference in terms of water pressure and availability at the taps is considerable. However, unvented cylinders are not without their challenges.

Unless they’re properly maintained and inspected every year, they can develop leaks that compromise performance and may damage wood and other materials in the surrounding area. In this post, we’ll look at some of the most common causes that lead to a water heater leaking.

Normal Expansion and Contraction

While you might think the walls of your cylinder are static, the fact is that metal expands and contracts with heat and pressure. When your cylinder is full of hot water and is at full pressure, the walls bow outward slightly. They contract as the water temperature drops through use and as cold water from the mains flows in. This expansion and contraction cycle can create small drips through the tundish, but it is normal.

Mains Pressure

The pressure within your unvented cylinder is created by two things – heat and the flow of water from the mains. If your mains water pressure is too high, it can cause an overpressure situation within your cylinder. While your mains pressure will usually remain about the same at all times, some situations can cause it to rise, which can then cause the pressure relief valve to open and water to flow through the tundish.

Cylinder Pressure

If your cylinder experiences high pressure, it may begin to leak. You’ll see a constant flow of water through the tundish. Some of the more common causes of high pressure within an unvented cylinder include a faulty pressure-reducing valve or expansion vessel, or improper pressure settings for the system. Do not attempt to adjust the pressure or replace a faulty valve on your own. Contact a G3-qualified engineer.

Temperature and Pressure Relief Valve

Unvented cylinders are designed with safety in mind. The temperature and pressure relief valve (TPRV) is designed to open if the cylinder’s temperature or pressure rises too high to prevent an explosion. However, these valves wear over time. They can also fail outright. In those cases, they may stick open, which will allow water to flow out and through the tundish. Again, do not attempt to replace the valve on your own. Only a G3-qualified engineer should handle repairs or replacements.

Damage to the Cylinder

The most catastrophic reason for seeing water around your water heater is damage to the cylinder. Aging cylinders can rust through, but any cylinder can be damaged through impacts and other events, leading to punctures. In these situations, the system needs to be turned off. Call a qualified engineer or plumber immediately.

Is your unvented cylinder leaking? Are you noticing water flowing through the tundish? Have you spotted water on the sides of the cylinder (condensation) or on the floor nearby? Leaks can be dangerous – contact EasyFlow to schedule an inspection by one of our G3-qualified engineers.


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