The Baxi Megaflo System is a range of wall-hung gas system boilers that work with a hot water cylinder. They suit homes with two or more bathrooms and high hot water demand. The range came in five outputs, from 15kW to 32kW, and was made to pair with Megaflo unvented cylinders.
Baxi no longer sells it. The 600 System 2 and 800 System 2 have taken its place. This review covers what the Megaflo System offers if you already own one, and what to look at when it’s time for a replacement.
What Are The Key Specs Of The Baxi Megaflo System?
It’s an A-rated gas condensing system boiler with 16.2kW to 34.4kW maximum heating output, depending on the model, and around 88.5% seasonal efficiency.
| Specification | Baxi Megaflo System |
| Boiler type | Gas condensing system boiler, wall-mounted |
| Models | 15, 18, 24, 28 and 32 |
| Max central heating output | 16.2kW to 34.4kW depending on model |
| Hot water | Supplied by a separate cylinder, so flow depends on the cylinder and mains supply |
| ErP rating | A (heating) |
| Seasonal efficiency | Around 88.5% |
| Dimensions (H x W x D) | 780 x 450 x 345mm (all models) |
| Fuel | Natural gas |
| Status | Discontinued. Replaced by the Baxi 600 System 2 and 800 System 2 |
What Is The Baxi Megaflo System Boiler?
It’s a system boiler, which means it heats your radiators directly and heats stored water in a cylinder, usually in an airing cupboard.
Unlike a combi, it doesn’t heat water on demand. The upside is that several taps and showers can run at once without the flow dropping off, as long as the cylinder is big enough.
The range takes its name from the Megaflo unvented cylinder, which is part of the same group, and the two were built to work together. You could also pair the boiler with other unvented or vented cylinders, and with Solarflo solar thermal systems.
Each model has the pump, expansion vessel and pressure relief valve built in. That leaves fewer separate parts to fit and maintain than a regular heat-only boiler. If you’re not sure which type of boiler suits your home, our guide to the types of boilers explains the differences.
Which Megaflo System Models Were Made?
Baxi made five models: the 15, 18, 24, 28 and 32. They share the same casing and features. The number in the name is the nominal heating output, and the maximum output is a little higher when the boiler is condensing.
| Model | Max Heating Output | Typically Suits |
| Megaflo System 15 | 16.2kW | Smaller homes and flats with a cylinder |
| Megaflo System 18 | 19.4kW | Small to medium homes |
| Megaflo System 24 | 25.9kW | Medium homes, often three bedrooms |
| Megaflo System 28 | 30.3kW | Larger homes with two bathrooms |
| Megaflo System 32 | 34.4kW | Large homes with high heat loss |
Treat these as rough guides. We size a system boiler on your home’s heat loss, not the number of bedrooms.
What Features Does The Megaflo System Have?
Its main features are a stainless steel heat exchanger and a built-in pump, expansion vessel and pressure relief valve, plus frost protection and an automatic bypass.
- Stainless steel heat exchanger: a hard-wearing choice for condensing boilers.
- Built-in pump, expansion vessel and pressure relief valve: simpler installation and no feed and expansion tank in the loft.
- Built-in frost thermostat: protects the boiler in very cold weather.
- Integral automatic bypass: protects the boiler when radiator valves close.
- Pre-plumbing jig: lets pipework be prepared before the boiler is hung.
- Controls: works with standard programmers, cylinder thermostats and on/off smart thermostats. See our smart thermostats page for options that can also manage hot water timing.
How Efficient Is The Megaflo System?
It’s ErP A-rated for heating, with a seasonal efficiency of around 88.5% on Baxi’s published figures. That’s close to what many current gas system boilers achieve.
With a system boiler, the cylinder affects running costs too. A well-insulated modern unvented cylinder loses less heat than an old copper tank. Timing your hot water around your routine also stops you heating water you don’t use.
Moving from an older, non-condensing boiler to a condensing model like the Megaflo System, or one of its replacements, will cut gas use.
Once a Megaflo System is over 8 years old, though, it’s usually less efficient and more likely to develop faults. At that age, a newer system boiler is often the better option.
What Are The Pros And Cons Of The Megaflo System?
The big advantage is plenty of hot water for several outlets at once. The drawbacks are that it’s discontinued and you need room for a cylinder.
Pros
- Handles several showers and taps running at once
- Five outputs, from 15kW up to 32kW
- A-rated for heating
- Pump, expansion vessel and safety valve built in
- Made to pair with Megaflo unvented cylinders
- Parts widely available and well known to engineers
Cons
- Discontinued, so not available for new installations
- Needs space for a hot water cylinder
- Stored hot water can run out if the cylinder is too small
- Larger casing than newer system boilers (780mm tall compared with 700mm for the 600 System 2)
- Costs more to install than a combi when converting, because of the cylinder
What Size Home Does The Megaflo System Suit?
It suits homes with two or more bathrooms, bigger families and anywhere hot water gets used in more than one place at a time.
Picture a four-bedroom house where one person is in the shower, another is running a bath and someone else is washing up. That’s where a cylinder earns its keep.
The 15 and 18 models suit smaller homes that already have a cylinder, while the 28 and 32 are aimed at larger detached homes.
In a flat or a one-bathroom home, a combi is usually cheaper to install and saves space. Our round-up of the best system boilers covers current models for larger homes.
How Much Does A Megaflo System Replacement Cost In 2026?
As a guide, swapping a Megaflo System for a new system boiler and keeping your cylinder costs around £2,300 to £3,200 installed. Because the Megaflo System is discontinued, that price is for a current model such as the Baxi 600 System 2 or 800 System 2.
The ranges below include the boiler, flue, magnetic filter, system flush and labour. Prices vary with your home and the work involved.
| Type Of Job | Guide Price Range (Installed) |
| Like-for-like system boiler swap, keeping the existing cylinder | £2,300 to £3,200 |
| System boiler with a new unvented cylinder | £3,500 to £5,000 |
| Converting a regular boiler and loft tanks to a system boiler and unvented cylinder | £4,000 to £5,500 |
A new unvented cylinder adds cost. You’re paying for the cylinder itself plus the extra pipework and safety equipment it needs.
For more on pricing, read how much a new boiler costs, or see our guide to boilers on finance if you’d prefer to spread the cost.
What Are The Best Alternatives To The Megaflo System?
The Baxi 600 System 2 is the most direct replacement, and it still works with Megaflo cylinders. The main options are:
- Baxi 600 System 2: available in 15, 18 and 24kW. It’s smaller and lighter than the Megaflo System, and still made to work with Megaflo cylinders.
- Baxi 800 System 2: available in 18, 24 and 30kW, with a system filter included. A good fit if you need more output.
- Worcester Bosch Greenstar system boilers: a popular choice if you prefer Worcester Bosch. Our Baxi vs Worcester Bosch guide compares the two brands.
- Vokera Evolve 30S: another system boiler option. Read our Vokera Evolve 30S review.
Baxi’s current system boilers stop at 30kW. If you’ve got a Megaflo System 32 in a large home, your installer should check the heat loss before recommending a replacement. You can read more about the brand in our Baxi boilers review.
Is The Baxi Megaflo System Worth It?
It was a reliable, efficient system boiler for larger homes, but once yours is over 8 years old, replacing it is usually the better option.
If yours is younger than that and serviced every year, there’s no need to replace it just because it’s discontinued.
When it passes 8 years old or starts developing faults, a current system boiler matched to your existing cylinder is usually the simplest upgrade.
Choose a system boiler like this if:
- Your home has two or more bathrooms
- Several people need hot water at the same time
- You already have a cylinder in good condition
- You’re a landlord with a larger rental property
Look elsewhere if:
- You live in a flat or one-bathroom home
- You haven’t got space for a cylinder
- You want the lowest possible installation cost
- Your home needs more than 30kW and you want to stay with Baxi
Get A Free Boiler Quote From Clever Energy Boilers
Clever Energy Boilers replaces system boilers and cylinders for homeowners and landlords across the North West, Yorkshire and the Midlands. Our experienced, professional and registered installers check your heating and hot water needs, then recommend the right boiler and cylinder so you’re not paying for more than you need.
Prices are fixed and transparent. When we handle your new boiler installation, long, market-leading warranties are available through Clever Energy.
Get a free online boiler quote to see what replacing your system boiler would cost.
Frequently Asked Questions
Is The Baxi Megaflo System Boiler Discontinued?
Yes. The Megaflo System range is no longer in Baxi’s line-up and has been replaced by the 600 System 2 and 800 System 2. Spare parts are still widely available.
Can I Keep My Existing Cylinder When Replacing A Megaflo System Boiler?
Often, yes, if the cylinder is in good condition and the right size for your household. An engineer will check its condition, insulation and controls before advising whether to keep or replace it.
What Size Hot Water Cylinder Do I Need?
Around 150 litres suits two or three people with one bathroom, as a rough guide. Four or more people, or homes with two bathrooms, usually need 210 litres or more. Your installer should size it to how your household actually uses hot water.
How Long Does A Baxi Megaflo System Boiler Last?
Many keep running past 10 years, but by around 8 years old efficiency has usually dropped and faults become more common. At that point, replacing it is often better value than paying for repairs. Annual servicing helps it run safely and efficiently in the meantime, and our Clever Care servicing plans keep that simple.
Does The Megaflo System Work With Smart Thermostats?
Yes, it works with standard on/off smart thermostats. Some smart controls can also manage hot water timing, which is handy with a cylinder.