Head to head
Vaillant ecoFIT pure 825 25kW combi vs Viessmann Vitodens 100-W 35kW combi
The Vaillant ecoFIT pure 825 25kW combi comes with 5 years more warranty. The Viessmann Vitodens 100-W 35kW combi puts out 13kW more to the radiators and runs 6.6 litres a minute more hot water.
Last reviewed 13 September 2026
Key differences
- Warranty: the Vaillant ecoFIT pure 825 25kW combi comes with 5 years more warranty.
- Central heating output: the Viessmann Vitodens 100-W 35kW combi puts out 13kW more to the radiators.
- Hot water flow rate: the Viessmann Vitodens 100-W 35kW combi runs 6.6 litres a minute more hot water.
- Hot water output: the Viessmann Vitodens 100-W 35kW combi has 10kW more hot water output.
- Seasonal efficiency: the Viessmann Vitodens 100-W 35kW combi is 4 points more efficient.
Specifications side by side
| Vaillant ecoFIT pure 825 25kW combi | Viessmann Vitodens 100-W 35kW combi | |
|---|---|---|
| Hot water output | 25.2 kW | 34.9 kW |
| Central heating output | 19.1 kW | 32 kW |
| ErP class | A | A |
| Seasonal efficiency | 94% | 98% |
| Dimensions | 700 x 390 x 295 mm | 700 x 400 x 360 mm |
| Weight | 32 kg | 35 kg |
| Warranty | 10 years when installed by Vaillant Advance installer | 5 years |
| Hot water flow rate | 10.4 litres per minute | 17 litres per minute |
Sources: Vaillant ecoFIT pure 825 25kW combi, Viessmann Vitodens 100-W 35kW combi. Figures vary by model year and options, so check with the supplier before you commit.
Buy or hire the ecoFIT pure 825 25kW combi if...
- you want one that comes with 5 years more warranty
A gas combi boiler with 25.2 kW of hot water output, sized for a flat or small house with one bathroom. It delivers about 10.4 litres per minute of hot water, which decides how well a shower runs while a tap is on. Warranty: 10 years when installed by Vaillant Advance installer. Seasonal efficiency is 94%.
Full ecoFIT pure 825 25kW combi specifications →Buy or hire the Vitodens 100-W 35kW combi if...
- you want one that puts out 13kW more to the radiators
- you want one that runs 6.6 litres a minute more hot water
- you want one that has 10kW more hot water output
- 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 →Common questions
What is the difference between the Vaillant ecoFIT pure 825 25kW combi and the Viessmann Vitodens 100-W 35kW combi?
The Vaillant ecoFIT pure 825 25kW combi comes with 5 years more warranty. The Viessmann Vitodens 100-W 35kW combi puts out 13kW more to the radiators and runs 6.6 litres a minute more hot water. The Vaillant ecoFIT pure 825 25kW combi is a gas combi boiler, 25.2 kW hot water output; the Viessmann Vitodens 100-W 35kW combi is a gas combi boiler, 34.9 kW hot water output.
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