Head to head
NIBE S2125 Model 12 vs Vaillant ecoFIT pure 835 35kW combi
The NIBE S2125 Model 12 is a air/water heat pump, up to 8.4 kw heat output. The Vaillant ecoFIT pure 835 35kW combi is a gas combi boiler, 35 kw hot water output.
Last reviewed 13 September 2026
Specifications side by side
| NIBE S2125 Model 12 | Vaillant ecoFIT pure 835 35kW combi | |
|---|---|---|
| Dimensions | 1070 x 1130 x 820 mm (H x W x D) | 700 x 390 x 295 mm |
| Weight | 160 kg | 33 kg |
| Heat output | 6.80-7.60 kW (average climate), 8.4 kW (cold climate) | - |
| SCOP | 5.0 at 35C, 3.8 at 55C (average climate); 4.2 at 35C, 3.4 at 55C (cold climate) | - |
| Sound power | 49 dB(A) at nominal rating (EN12102) | - |
| Max flow temperature | up to 75C | - |
| Hot water output | - | 35 kW |
| Central heating output | - | 26.7 kW |
| ErP class | - | A |
| Seasonal efficiency | - | 94% |
| Warranty | - | 10 years when installed by Vaillant Advance installer |
| Hot water flow rate | - | 14.1 litres per minute |
Sources: NIBE S2125 Model 12, 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 S2125 Model 12 if...
The larger NIBE S2125, sized for a medium house and rated to hold output down to -25C outdoor temperature. It shares its cabinet size with the smaller model but weighs 10 kg more for the larger compressor.
Full S2125 Model 12 specifications →Buy or hire the ecoFIT pure 835 35kW combi if...
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 NIBE S2125 Model 12 and the Vaillant ecoFIT pure 835 35kW combi?
The NIBE S2125 Model 12 is a air/water heat pump, up to 8.4 kW heat output; the Vaillant ecoFIT pure 835 35kW combi is a gas combi boiler, 35 kW hot water output.
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