The Worcester Bosch Greenstar Highflow 440CDi is a floor-standing gas combi with a built-in thermal store. It gives up to 20 litres per minute of mains-pressure hot water and fits under a standard kitchen worktop, which made it a favourite for larger homes.
Worcester has discontinued the Highflow CDi range. Its replacement is the Greenstar 8000 F floor-standing combi, launched in late 2025. This review is for homeowners and landlords who already have a 440CDi, and for anyone deciding what should replace one.
What Are The Worcester Highflow 440CDi’s Key Specs?
The 440CDi gives up to 29.2kW of heating and 20 l/min of hot water at a 35°C rise. It’s discontinued and replaced by the Greenstar 8000 F.
| Specification | Greenstar Highflow 440CDi |
| Boiler type | Floor-standing condensing combi with integral thermal store |
| Central heating output | 7.4kW to 29.2kW |
| Hot water flow rate | 20 l/min at a 35°C rise |
| ErP heating rating | A (92% seasonal efficiency) |
| Dimensions (H x W x D) | 850mm x 600mm x 600mm |
| Dry weight | Around 112kg |
| Mains pressure needed for full flow | 1.5 bar |
| Fuel | Natural gas, with an LPG version |
| Status | Discontinued. Replaced by the Worcester Bosch Greenstar 8000 F |
What Is The Worcester Bosch Highflow 440CDi?
It’s a floor-standing combi with a small thermal store inside, so it doesn’t work quite like the wall-hung combis most people know.
That store, sometimes called a heat bank, is kept hot by the boiler. When you open a tap, the stored water passes through a plate heat exchanger and warms the incoming mains water on its way to the outlet.
The result is a higher hot water flow than its 29.2kW heating output would suggest. It still runs at mains pressure, so there’s no cold water tank in the loft and no separate cylinder to find room for.
The Highflow range had two models. The 440CDi is the smaller one, and the Highflow 550CDi sits above it with up to 25 litres per minute.
What Features Does The Highflow 440CDi Have?
Its key feature is the built-in thermal store, which gives stronger hot water than a standard combi of the same heating size.
- Thermal store design: stored heat gives a stronger hot water flow than a standard combi with similar heating output.
- Mains-pressure hot water: good shower pressure without a pump, as long as your incoming supply is strong enough.
- Under-worktop size: 850mm high, 600mm wide and 600mm deep, so it fits a standard kitchen unit space.
- Room-sealed fanned flue: the compartment doesn’t need extra ventilation.
- LPG version: suitable for off-grid homes. See our LPG and oil boilers page.
- Control compatibility: works with most mechanical, digital and wireless controls.
How Efficient Is The Highflow 440CDi?
It’s A-rated for space heating, with a seasonal efficiency of 92%. Its earlier SEDBUK rating was 90.8% on natural gas.
Those figures are in line with current gas boilers. A working 440CDi isn’t an inefficient boiler.
There’s one running cost difference you should know about, though. The thermal store is kept hot so hot water is ready on demand, and that uses a little energy even when no taps are running. A standard instantaneous combi doesn’t have that standing loss.
In most homes the difference is small. Still, it’s one reason we find the Highflow suits busy households better than one or two people living alone.
As with any condensing boiler, a lower flow temperature, good controls and a clean system make the biggest difference to your bills. A smart thermostat can also help you heat the home only when you need it.
What Are The Pros And Cons Of The Highflow 440CDi?
The main pro is 20 l/min of hot water without a cylinder. The main cons are its weight, its floor space and the fact it’s no longer made.
Pros
- 20 l/min of hot water, well above most wall-hung combis
- No hot water cylinder or loft tank needed
- Fits under a kitchen worktop
- A-rated for space heating
- Made in natural gas and LPG versions
- Suits homes with up to three bathrooms
Cons
- Discontinued, so you can’t buy one new
- Heavy at around 112kg, which makes replacement a two-person job
- Takes up a full base unit of kitchen space
- Needs at least 1.5 bar of mains pressure to reach its rated flow
- Some standing heat loss from keeping the store hot
What Size Home Does The Highflow 440CDi Suit?
It suits three to four-bedroom homes with up to three bathrooms, especially where two showers are often used close together or a bath needs to fill quickly.
Mains supply is the deciding factor. Worcester’s figures call for 1.5 bar of incoming pressure for the 440CDi to deliver its full flow, and it needs at least 0.5 bar to work at all.
If your water pressure is low, a system boiler with an unvented cylinder may not fix things either. Get the supply tested first.
For homes where several showers run at once every morning, a system boiler with a large cylinder is usually the more reliable answer.
How Much Does It Cost To Replace A Highflow 440CDi In 2026?
Swapping a 440CDi for a Greenstar 8000 F floor-standing combi typically costs £4,000 to £6,200 fitted, depending on the size you choose.
Floor-standing combis cost more than wall-hung ones, for both the boiler and the labour. The ranges below are a guide only, and we price every job individually.
| Type Of Job | Typical Installed Price Range (Guide Only) |
| Swap to a Greenstar 8000 F 35kW floor-standing combi | £4,000 to £5,200 |
| Swap to a Greenstar 8000 F 50kW floor-standing combi | £4,800 to £6,200 |
| Replace with a wall-hung combi and free up the floor space | £3,000 to £4,500 |
| Convert to a system boiler and unvented cylinder | £4,500 to £6,500+ |
Prices depend on access, flue route, gas supply and how much pipework needs changing. Our guide to how much a new boiler costs explains what affects the final figure. You can also spread the cost with boiler finance.
What Are The Best Alternatives To The Highflow 440CDi?
The Worcester Bosch Greenstar 8000 F is the direct replacement, and its 50kW model is the closest match on hot water.
- Worcester Bosch Greenstar 8000 F: floor-standing, with the same 850mm x 600mm x 600mm footprint, in 35kW and 50kW combi versions. It comes with a pre-piping jig to make swaps from a Highflow CDi simpler. The 35kW is listed at around 14.2 l/min at a 35°C rise and the 50kW at around 19.8 l/min.
- Worcester Bosch Greenstar 8000+ Life: a wall-hung combi in sizes up to 50kW, if you’d rather free up the kitchen unit. Read our Greenstar 8000 Life and Style review.
- A system boiler and unvented cylinder: the best option for homes with heavy, simultaneous hot water use.
Is The Worcester Bosch Highflow 440CDi Worth It?
Yes, if yours is under 8 years old, reliable and serviced each year, it’s worth keeping. The 440CDi filled a real gap, giving more hot water than a normal combi without the space a cylinder takes.
Once it’s over 8 years old, replacing it is usually better value than paying for repairs, and the Greenstar 8000 F is the obvious like-for-like choice. Some homes will be better off with a wall-hung combi or a cylinder system, though.
Choose A Highflow-Style Floor-Standing Combi If:
- You have a large home with two or three bathrooms
- You have a spare base unit in the kitchen or utility room
- Your mains water pressure is at least 1.5 bar
Look Elsewhere If:
- Your mains pressure or flow is poor
- You need the floor space back
- Several showers often run at exactly the same time
Get A Free Boiler Quote From Clever Energy Boilers
Clever Energy Boilers fits new Worcester Bosch boiler installations, including floor-standing models, for homeowners and landlords across the North West, Yorkshire and the Midlands. As Worcester Bosch accredited installers, we’ll check your water pressure and gas supply before recommending a replacement for your Highflow.
Long, market-leading warranties are on offer through Clever Energy for the boilers we fit. Our Clever Care servicing plans keep everything running after that.
Start with a free, fixed-price boiler quote online.
Frequently Asked Questions
Is The Worcester Highflow 440CDi Discontinued?
Yes, Worcester has discontinued the Highflow CDi range. The Greenstar 8000 F floor-standing combi, launched in late 2025, is its replacement.
What Is The Flow Rate Of The Highflow 440CDi?
It’s up to 20 litres per minute at a 35°C rise. The boiler needs 1.5 bar of mains pressure to reach that figure.
Does The Highflow 440CDi Need A Hot Water Cylinder?
No, the 440CDi is a combi and heats mains water as you use it. Its built-in thermal store is part of the boiler, not a separate cylinder.
Can The Highflow 440CDi Run On LPG?
Yes, Worcester made the 440CDi in natural gas and LPG versions. Any LPG work must be done by a Gas Safe registered engineer qualified for LPG.
How Long Does It Take To Replace A Highflow 440CDi?
A like-for-like swap to a floor-standing combi usually takes one to two days. Moving the boiler or converting to a different system can take longer.