Head to head
Vaillant ecoFIT pure 825 25kW combi vs Vaillant ecoFIT pure 835 35kW combi
The Vaillant ecoFIT pure 835 35kW combi puts out 8kW more to the radiators and has 10kW more hot water output.
Last reviewed 13 September 2026
Key differences
- Central heating output: the Vaillant ecoFIT pure 835 35kW combi puts out 8kW more to the radiators.
- Hot water output: the Vaillant ecoFIT pure 835 35kW combi has 10kW more hot water output.
- Hot water flow rate: the Vaillant ecoFIT pure 835 35kW combi runs 3.7 litres a minute more hot water.
Specifications side by side
| Vaillant ecoFIT pure 825 25kW combi | Vaillant ecoFIT pure 835 35kW combi | |
|---|---|---|
| Hot water output | 25.2 kW | 35 kW |
| Central heating output | 19.1 kW | 26.7 kW |
| ErP class | A | A |
| Seasonal efficiency | 94% | 94% |
| Dimensions | 700 x 390 x 295 mm | 700 x 390 x 295 mm |
| Weight | 32 kg | 33 kg |
| Warranty | 10 years when installed by Vaillant Advance installer | 10 years when installed by Vaillant Advance installer |
| Hot water flow rate | 10.4 litres per minute | 14.1 litres per minute |
Sources: Vaillant ecoFIT pure 825 25kW combi, Vaillant ecoFIT pure 835 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...
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 ecoFIT pure 835 35kW combi if...
- you want one that puts out 8kW more to the radiators
- you want one that has 10kW more hot water output
- you want one that runs 3.7 litres a minute more hot water
A gas combi boiler with 35 kW of hot water output, sized for a larger house with two bathrooms. It delivers about 14.1 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 835 35kW combi specifications →Common questions
What is the difference between the Vaillant ecoFIT pure 825 25kW combi and the Vaillant ecoFIT pure 835 35kW combi?
The Vaillant ecoFIT pure 835 35kW combi puts out 8kW more to the radiators and has 10kW more hot water output. The Vaillant ecoFIT pure 825 25kW combi is a gas combi boiler, 25.2 kW hot water output; the Vaillant ecoFIT pure 835 35kW combi is a gas combi boiler, 35 kW hot water output.
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