James Elston

James Elston

Published February 23, 2024

The Megaflow system, also known as the Megaflo system, is an unvented hot water cylinder manufactured by Heatrae Sadia. The Megaflow system is often confused with the unvented boiler system; however, Megaflow systems function specifically as hot water cylinders and require the installation of a system boiler.

The system is popular with many homeowners and plays a big role in central heating. This article aims to provide a detailed understanding of the Megaflow system, how it works, and its benefits and drawbacks.

Understanding Megaflow Systems

The Megaflow system is a stainless steel unvented cylinder that stores hot water as part of the central heating system. It uses the mains water pressure to provide a continuous flow of hot water throughout your property.

A Megaflow does not require a cold water tank or vent pipe to release air, saving space and reducing water contamination. The Megaflow’s safety features include:

  • Expansion relief valve removes water when there is too much heat, and the system fails. Sometimes, this valve is combined with the pressure-relief valve to create one device that controls water flow into the system.
  • The temperature pressure relief valve (TPR) controls the temperature and pressure in the hot water tanks.
  • Tundish: Both valves use a discharge pipe and Tundish to release water stored during a fault.

Installation Requirements And Process

Installing a Megaflow system must be done by a licensed gas-safe engineer with an unvented hot water qualification. This is due to the legal requirements for all unvented systems under Building Regulation G3.

Installing an unvented cylinder involves numerous steps, depending on whether it is a direct or indirect system. The process starts with carefully checking the existing heating system and infrastructure to find potential hazards before connecting it to the main water supply.

The Megaflow includes a comprehensive 25-year warranty, including warranties that cover various components like the hot water tank and control valves.

Installation costs of the Megaflow will vary depending on the size of the cylinder and labour costs. However, you can expect to pay between £500 and £1500.

Megaflow System Considerations

Here are a few considerations to take into account:

Compatibility and integration

There are different Megaflow cylinders. You would need to find compatible unvented cylinder models to integrate with a renewable energy source. For example, solar cylinders come with a specific heating coil designed to harness energy from the sun. Others may have an extra coil that connects to system boilers with electric heating elements for backup heating.

Choosing the right model

Selecting the correct model is crucial and depends on factors like the size of your home, how much hot water you need, and whether it is compatible with your existing heating systems.

There are two types of unvented systems: direct and indirect cylinders. Direct cylinders use an electric immersion heater and do not use gas, oil, or heat pump systems. Indirect cylinders have a coil running through it that heats the water as it flows through the coil.

Common issues and troubleshooting

The Megaflow cylinder is dependable but not without fault. Common issues include:

  • Compatibility issues with older radiators in the home.
  • The need for combi boilers for the mains supply.
  • Drops are water temperature and pressure.

Costs and budgeting

There are several factors to consider and how they impact the installation cost. Various elements, such as the size, capacity, brand, and complexity of installing the cylinder, should be planned and budgeted for.

Storage water heaters that can meet the demand usually have higher initial costs. However, over time, the energy efficiency, reliability, and constant hot water supply make up for these costs.

The Advantages Of A Megaflow System

As a popular brand providing hot water to every tap, here are a few advantages of the Megaflow System:

1. Strong water pressure

The Heatrae Sadia Megaflo hot water cylinder is designed to deliver strong and consistent water pressure. This feature means you do not lose water pressure if used in multiple areas in your home.

2. Compatible with renewable energy resources

The Megaflow can be integrated with renewable energy sources, such as solar thermal energy systems, solar panels, biomass, and heat pumps.

3. Hot water storage capacity

Both direct and indirect Megaflow cylinder storage capacity ranges from 70L to 300L, ensuring ample supply for larger households.

4. No risk of contamination

Unvented cylinders do not have a cold water storage tank which eliminates the risk of contamination, ensuring your water remains clean and safe for domestic use.

The Disadvantages Of The Megaflow System

Megaflow systems are dependable; however, they are not perfect. Here are some disadvantages to take into consideration:

Requires professional installation

Due to the intricacies of installation and the legal requirements for gas-unvented boiler systems and water tanks, a registered gas-safe engineer must do the installation.

Requires regular maintenance

The Megaflow system is a high-quality product that requires little to no maintenance. However, the internal air gap needs recharging regularly, the safety valves could fail, or the Tundish could leak.


How long does a Megaflow last?

Most hot water cylinders have a lifespan of ten years, but a Megaflow System can last up to 25 years if well-maintained.

How long does it take to heat water in a Megaflow?

Megaflow unvented cylinders take 30 to 40 minutes to heat water from cold to hot. The heating time will depend on the size of the unvented cylinder.

Why is there no hot water in my Megaflow?

There are several reasons why a Megaflow might not provide hot water, including an electrical fault, the immersion heater failing, or a thermal trip in the thermostat head.

How do I turn off Megaflow?

To turn off the Megaflow system, first turn off the mains water supply by the cylinder before turning off the valve on the cold water combination valve.

Final Thoughts

The Megaflow unvented cylinders are ideal for households requiring significant hot water to meet their needs. This system effectively distributes hot water throughout your property, making it a valuable addition to any central heating system.

James Elston

James Elston

Boiler Expert

James Elston is the top boiler replacement and heating expert at Eco Happy. He has over 20 years of experience in the industry, focusing on Gas Safe boiler installations and offering home-heating and energy-saving solutions to homeowners across the UK. From sourcing the most energy-efficient combi boiler to providing specialist heating advice, James ensures that Eco Happy maintains the highest standards and best customer service.

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