Head to head
Viessmann Vitodens 100-W 35kW combi vs Worcester Bosch Greenstar 4000 25kW combi
The Worcester Bosch Greenstar 4000 25kW combi comes with 5 years more warranty. The Viessmann Vitodens 100-W 35kW combi runs 6.5 litres a minute more hot water and has 10kW more hot water output.
Last reviewed 13 September 2026
Key differences
- Warranty: the Worcester Bosch Greenstar 4000 25kW combi comes with 5 years more warranty.
- Hot water flow rate: the Viessmann Vitodens 100-W 35kW combi runs 6.5 litres a minute more hot water.
- Hot water output: the Viessmann Vitodens 100-W 35kW combi has 10kW more hot water output.
- Central heating output: the Viessmann Vitodens 100-W 35kW combi puts out 7kW more to the radiators.
- Seasonal efficiency: the Viessmann Vitodens 100-W 35kW combi is 4 points more efficient.
Specifications side by side
| Viessmann Vitodens 100-W 35kW combi | Worcester Bosch Greenstar 4000 25kW combi | |
|---|---|---|
| Hot water output | 34.9 kW | 25 kW |
| Central heating output | 32 kW | 25 kW |
| ErP class | A | A |
| Seasonal efficiency | 98% | 94% |
| Dimensions | 700 x 400 x 360 mm | 710 x 400 x 310 mm |
| Weight | 35 kg | 32.0 kg |
| Warranty | 5 years | 10 years |
| Hot water flow rate | 17 litres per minute | 10.5 litres per minute |
Sources: Viessmann Vitodens 100-W 35kW combi, Worcester Bosch Greenstar 4000 25kW combi. Figures vary by model year and options, so check with the supplier before you commit.
Buy or hire the Vitodens 100-W 35kW combi if...
- you want one that runs 6.5 litres a minute more hot water
- you want one that has 10kW more hot water output
- you want one that puts out 7kW more to the radiators
- you want one that is 4 points more efficient
A gas combi boiler with 34.9 kW of hot water output, sized for a larger house with two bathrooms. It delivers about 17 litres per minute of hot water, which decides how well a shower runs while a tap is on. Warranty: 5 years. Seasonal efficiency is 98%.
Full Vitodens 100-W 35kW combi specifications →Buy or hire the Greenstar 4000 25kW combi if...
- you want one that comes with 5 years more warranty
A gas combi boiler with 25 kW of hot water output, sized for a flat or small house with one bathroom. It delivers about 10.5 litres per minute of hot water, which decides how well a shower runs while a tap is on. Warranty: 10 years. Seasonal efficiency is 94%.
Full Greenstar 4000 25kW combi specifications →Common questions
What is the difference between the Viessmann Vitodens 100-W 35kW combi and the Worcester Bosch Greenstar 4000 25kW combi?
The Worcester Bosch Greenstar 4000 25kW combi comes with 5 years more warranty. The Viessmann Vitodens 100-W 35kW combi runs 6.5 litres a minute more hot water and has 10kW more hot water output. The Viessmann Vitodens 100-W 35kW combi is a gas combi boiler, 34.9 kW hot water output; the Worcester Bosch Greenstar 4000 25kW combi is a gas combi boiler, 25 kW hot water output.
GetBrent is an independent directory and is not a dealer for, nor affiliated with, either manufacturer. Model and brand names are the trademarks of their owners.