The Baxi Duo-tec 28 is a 28kW gas combi that suits homes with one bathroom and around 10 to 15 radiators. It’s an A-rated condensing boiler with an 11.5 litre per minute hot water flow rate, and for years it was one of Baxi’s most widely fitted mid-range models.
You can’t buy one new any more, as Baxi’s 600 Combi 2 and 800 Combi 2 ranges have taken its place. This review is for homeowners and landlords who already have a Duo-tec 28, and for anyone deciding what to replace it with.
What Are The Key Specs Of The Baxi Duo-tec 28?
The Duo-tec 28 gives 28kW for hot water, 25.9kW for heating and 11.5 l/min at a 35°C rise, with an ErP A rating and 89% seasonal efficiency.
| Specification | Baxi Duo-tec Combi 28 |
| Boiler type | Gas condensing combi, wall-mounted |
| Hot water output | 28kW |
| Max central heating output | 25.9kW |
| Hot water flow rate (35°C rise) | 11.5 l/min |
| ErP rating | A (heating and hot water) |
| Seasonal efficiency | 89% |
| Dimensions (H x W x D) | 780 x 450 x 345mm |
| Fuel | Natural gas (separate LPG version made) |
| Status | Discontinued. Closest current replacements are the Baxi 630 Combi 2 and 830 Combi 2 |
What Is The Baxi Duo-tec 28?
It’s the middle model in Baxi’s old Duo-tec combi range, which also came in 24kW, 33kW and 40kW versions. It sat above Baxi’s entry-level combis and below the more premium Platinum models.
For several years it was a go-to for installers who wanted a reliable boiler at a sensible price.
Like all combis, it heats water from the mains on demand, so you don’t need a hot water cylinder or loft tanks. Baxi has built boilers in Britain for well over a century, with its main factory in Preston, Lancashire. Parts for the Duo-tec are still easy to find, and most engineers know it well.
What Features Does The Duo-tec 28 Have?
Its main features are a stainless steel heat exchanger, built-in frost protection, an automatic bypass and a fault code display. Most of them make servicing and repairs easier too:
- Stainless steel heat exchanger: a hard-wearing material that copes well with the condensing process.
- Pre-plumbing jig: supplied with the boiler so pipework could be prepared before the boiler went on the wall.
- Built-in frost thermostat: fires the boiler to protect it if the temperature drops very low.
- Integral automatic bypass: protects the boiler when radiator valves close.
- Status and fault display: shows temperatures and fault codes to help with diagnosis.
- Controls: can take an integral mechanical timer and works with standard room thermostats and on/off smart thermostats. Our Hive vs Nest guide compares two popular options.
How Efficient Is The Duo-tec 28?
It’s ErP A-rated for heating and hot water, with a seasonal efficiency of 89% on Baxi’s published figures. That’s typical for gas combis of its generation and close to many current models.
If your Duo-tec replaced a much older, non-condensing boiler, you’ll already be using less gas for the same warmth.
Most Duo-tecs are now well over 8 years old, though, and by that age efficiency has usually dropped and faults are more common. A lower flow temperature, better controls and a clean system help, but a new combi is usually the better long-term option.
What Are The Pros And Cons Of The Duo-tec 28?
Its strengths are an A rating, a decent heating output and parts that are easy to find. On the downside, it’s no longer sold, the hot water flow is modest and the casing is bulky.
Pros
- A-rated for heating and hot water
- 25.9kW heating output suits most mid-sized homes
- Stainless steel heat exchanger
- Built-in frost protection and automatic bypass
- Parts widely available and well known to engineers
- LPG version made for homes off the gas grid
Cons
- Discontinued, so you can’t buy a new one for a fresh installation
- 11.5 l/min hot water flow is modest for a 28kW combi
- Larger and heavier than newer Baxi combis (780mm tall and 345mm deep, compared with 700 x 285mm for the 600 Combi 2)
- Not suited to two bathrooms used at the same time
- At this age, parts such as fans, diverter valves or PCBs can need replacing as they wear
What Size Home Does The Duo-tec 28 Suit?
It suits a mid-sized semi or terraced home with one bathroom and roughly 10 to 15 radiators. Its 25.9kW heating output covers the heat loss of most homes that size.
Hot water is the limit.
At 11.5 litres per minute it handles one shower well, but if someone runs the kitchen tap while you’re showering, both will drop. If you’ve got two bathrooms in regular use, a higher output combi or a system boiler with a cylinder is a better match. Our guide on how to size a combi boiler explains how to pick the right output.
How Much Does It Cost To Replace A Duo-tec 28 In 2026?
As a guide, replacing a Duo-tec 28 with a new combi in the same spot costs around £1,800 to £2,600 installed. Since the Duo-tec is discontinued, that price is for a current mid-range combi such as the Baxi 630 Combi 2.
The guide ranges below include the flue, magnetic filter, system flush and labour. Every home is different, so your quote may sit outside them.
| Type Of Job | Guide Price Range (Installed) |
| Replacing a Duo-tec 28 with a new combi in the same position | £1,800 to £2,600 |
| Combi replacement with the boiler moved | £2,400 to £3,300 |
| Converting a system or regular boiler to a combi | £2,800 to £4,000 |
A like-for-like swap from a Duo-tec is usually straightforward. The newer boiler is smaller, though, so the installer may need to adapt pipework and tidy the area the bigger casing used to cover. For more detail, read how much a new boiler costs.
What Are The Best Alternatives To The Duo-tec 28?
The Baxi 630 Combi 2 is the closest like-for-like replacement for a Duo-tec 28. These current boilers are all worth a look:
- Baxi 630 Combi 2: the closest modern equivalent. It’s smaller and lighter, and gives 12.2 l/min of hot water. See our Baxi 630 Combi review.
- Baxi 830 Combi 2: Baxi’s higher-spec range if you want extra features.
- Worcester Bosch Greenstar 4000: a popular mid-range combi from a brand with a strong reputation for build quality. Our Baxi vs Worcester Bosch guide compares the two makers.
- Vaillant ecoTEC Pro 28: another long-running 28kW combi for one-bathroom homes. Read our Vaillant ecoTEC Pro 28 review.
Our list of the best combi boilers covers more options.
Is The Baxi Duo-tec 28 Worth It?
It’s been a solid combi for one-bathroom homes, but most are now over 8 years old, so a new boiler is usually the better option.
If yours is still reliable, keep it serviced every year while you plan the change.
Once faults start to appear, it usually makes more sense to fit a current combi than to keep paying for repairs on an ageing boiler.
Keep or choose a similar boiler if:
- Your home has one bathroom and 10 to 15 radiators
- Your current Duo-tec is reliable and serviced every year
- You want a like-for-like combi at a mid-range price
- You’re a landlord after an easy-to-maintain boiler for a mid-sized rental
Look elsewhere if:
- Two bathrooms in your home get used at the same time
- Your Duo-tec is over 8 years old or starting to develop faults
- You’d like a smaller boiler that fits neatly in a kitchen cupboard
- Your home loses heat quickly and needs more output
Get A Free Boiler Quote From Clever Energy Boilers
If your Duo-tec 28 is showing its age, we can replace it with a modern combi sized properly for your home. Our experienced, professional and registered installers work with homeowners and landlords across the North West, Yorkshire and the Midlands.
You’ll get a clear, fixed price with no hidden extras. Long warranty cover can be added through Clever Energy on our new boiler installations.
Start with a free online boiler quote. It only takes a few minutes.
Frequently Asked Questions
Is The Baxi Duo-tec 28 Still Available?
No. The Duo-tec range has gone from Baxi’s line-up, replaced by the 600 Combi 2 and 800 Combi 2 ranges. Spare parts for the Duo-tec are still widely available.
What Is The Flow Rate Of The Baxi Duo-tec 28?
It’s 11.5 litres of hot water per minute at a 35°C temperature rise, which is enough for one shower at a time.
How Long Does A Baxi Duo-tec 28 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. Until then, an annual service by a Gas Safe registered engineer keeps it safe and efficient, and our Clever Care servicing plans make it easy to stay on top of.
Does The Baxi Duo-tec 28 Qualify For The Boiler Upgrade Scheme?
No. The Boiler Upgrade Scheme only supports low-carbon heating such as heat pumps and biomass boilers, not gas boilers. Help with replacing a gas boiler is limited and changes over time, so check GOV.UK for the schemes currently open in your area.
Is The Baxi Duo-tec 28 Suitable For A Rental Property?
Yes, it’s been a popular landlord choice for mid-sized rentals with one bathroom. You’ll need a Gas Safety check (CP12) every year, and any replacement should be fitted and commissioned by a Gas Safe registered engineer.