Head to head
Glow-worm Energy Combi 25C 25kW vs Vaillant ecoTEC plus 835 35kW combi
The Vaillant ecoTEC plus 835 35kW combi puts out 15kW more to the radiators and comes with 3 years more warranty.
Last reviewed 13 September 2026
Key differences
- Central heating output: the Vaillant ecoTEC plus 835 35kW combi puts out 15kW more to the radiators.
- Warranty: the Vaillant ecoTEC plus 835 35kW combi comes with 3 years more warranty.
- Hot water flow rate: the Vaillant ecoTEC plus 835 35kW combi runs 3.9 litres a minute more hot water.
- Hot water output: the Vaillant ecoTEC plus 835 35kW combi has 9kW more hot water output.
Specifications side by side
| Glow-worm Energy Combi 25C 25kW | Vaillant ecoTEC plus 835 35kW combi | |
|---|---|---|
| Hot water output | 25.7 kW | 35 kW |
| Central heating output | 18 kW | 32.8 kW |
| ErP class | A | A |
| Seasonal efficiency | 94% | 94% |
| Dimensions | 700 x 390 x 280 mm | 720 x 440 x 372 mm |
| Warranty | 7 years | 10 years with Vaillant Advance Boiler Protection Kit |
| Hot water flow rate | 10.4 litres per minute | 14.3 litres per minute |
| Weight | 32 kg | - |
Sources: Glow-worm Energy Combi 25C 25kW, Vaillant ecoTEC plus 835 35kW combi. Figures vary by model year and options, so check with the supplier before you commit.
Buy or hire the Energy Combi 25C 25kW if...
A gas combi boiler with 25.7 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: 7 years. Seasonal efficiency is 94%.
Full Energy Combi 25C 25kW specifications →Buy or hire the ecoTEC plus 835 35kW combi if...
- you want one that puts out 15kW more to the radiators
- you want one that comes with 3 years more warranty
- you want one that runs 3.9 litres a minute more hot water
- you want one that has 9kW more hot water output
A gas combi boiler with 35 kW of hot water output, sized for a larger house with two bathrooms. It delivers about 14.3 litres per minute of hot water, which decides how well a shower runs while a tap is on. Warranty: 10 years with Vaillant Advance Boiler Protection Kit. Seasonal efficiency is 94%.
Full ecoTEC plus 835 35kW combi specifications →Common questions
What is the difference between the Glow-worm Energy Combi 25C 25kW and the Vaillant ecoTEC plus 835 35kW combi?
The Vaillant ecoTEC plus 835 35kW combi puts out 15kW more to the radiators and comes with 3 years more warranty. The Glow-worm Energy Combi 25C 25kW is a gas combi boiler, 25.7 kW hot water output; the Vaillant ecoTEC plus 835 35kW combi is a gas combi boiler, 35 kW hot water output.
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