Head to head
Glow-worm Energy Combi 25C 25kW vs Viessmann Vitodens 100-W 35kW combi
The Viessmann Vitodens 100-W 35kW combi puts out 14kW more to the radiators and runs 6.6 litres a minute more hot water. The Glow-worm Energy Combi 25C 25kW comes with 2 years more warranty.
Last reviewed 13 September 2026
Key differences
- Central heating output: the Viessmann Vitodens 100-W 35kW combi puts out 14kW more to the radiators.
- Hot water flow rate: the Viessmann Vitodens 100-W 35kW combi runs 6.6 litres a minute more hot water.
- Warranty: the Glow-worm Energy Combi 25C 25kW comes with 2 years more warranty.
- Hot water output: the Viessmann Vitodens 100-W 35kW combi has 9kW more hot water output.
- Seasonal efficiency: the Viessmann Vitodens 100-W 35kW combi is 4 points more efficient.
Specifications side by side
| Glow-worm Energy Combi 25C 25kW | Viessmann Vitodens 100-W 35kW combi | |
|---|---|---|
| Hot water output | 25.7 kW | 34.9 kW |
| Central heating output | 18 kW | 32 kW |
| ErP class | A | A |
| Seasonal efficiency | 94% | 98% |
| Dimensions | 700 x 390 x 280 mm | 700 x 400 x 360 mm |
| Weight | 32 kg | 35 kg |
| Warranty | 7 years | 5 years |
| Hot water flow rate | 10.4 litres per minute | 17 litres per minute |
Sources: Glow-worm Energy Combi 25C 25kW, 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 Energy Combi 25C 25kW if...
- you want one that comes with 2 years more warranty
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 Vitodens 100-W 35kW combi if...
- you want one that puts out 14kW more to the radiators
- you want one that runs 6.6 litres a minute more hot water
- you want one that has 9kW 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 Glow-worm Energy Combi 25C 25kW and the Viessmann Vitodens 100-W 35kW combi?
The Viessmann Vitodens 100-W 35kW combi puts out 14kW more to the radiators and runs 6.6 litres a minute more hot water. The Glow-worm Energy Combi 25C 25kW comes with 2 years more warranty. The Glow-worm Energy Combi 25C 25kW is a gas combi boiler, 25.7 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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