This Viessman 20kw boiler review explores a compact, efficient gas condensing boiler ideal for small to medium UK homes and flats, offering strong value with premium German engineering.
Viessman 20kw Boiler Review: At a Glance
| Aspect | Details |
| Boiler Type | Wall-hung combi or system (gas condensing) |
| Outputs Available | 20kW (modulating 4.8–20kW) |
| Efficiency | Up to 98% (ErP A-rated) |
| Hot Water Flow Rate | 11.2 l/min (35°C rise) |
| Dimensions | 707 × 400 × 350 mm (Vitodens 050-W); ~36kg |
| Warranty | 7 years standard (extendable to 10 years with filter & registration) |
| Estimated Supply Cost | £650–£900 |
| Estimated Installed Cost | £1,800–£2,600 |
| Running Costs | £750–£1,050 annually (2–3 bedroom home) |
| Maintenance & Servicing | Annual Gas Safe service required |
| Trustpilot (Brand) | 4.3/5 (5,300+ reviews) |
| Which? (Brand) | 5/5 reliability; Best Buy status |
| Best Suited For | Small–medium homes, 1–2 bedrooms, 1 bathroom |
| Key Features | MatriX-Plus burner, Inox-Radial exchanger, weather compensation, ViCare app |
Viessmann’s 20kW boilers, such as the Vitodens 050-W and Vitodens 100-W, deliver reliable heating and hot water for modest properties with a focus on high efficiency and quiet operation.
Pros and Cons
Pros:
- Extremely quiet operation suitable for open-plan living
- Excellent build quality and corrosion-resistant components
- Smart app control and weather compensation
- Compact footprint for tight installations
- Strong efficiency and low emissions
Cons:
- Higher upfront cost than budget brands
- Limited to smaller properties (not ideal for large homes)
- Service network smaller than major UK brands
The Viessmann 20kW boiler stands out as a winner for pros and cons because its strengths in efficiency, quietness, and durability outweigh the higher initial cost for suitable properties.
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Viessman 20kw Efficiency
Efficiency in Viessmann 20kW boilers reaches up to 98% thanks to the MatriX-Plus burner and Inox-Radial stainless steel heat exchanger, which extract maximum heat from flue gases. The 1:10 modulation ratio ensures precise output, reducing cycling and energy waste.
Viessman 20kw Specs
Specs for the 20kW models include a modulation range down to 4.8kW, supporting up to 10–12 radiators, with compact dimensions ideal for cupboard installation. The lightweight design and low NOx emissions make them suitable for modern UK properties.
Viessman 20kw Features and Technology
Features and technology include weather compensation, the ViCare app for remote control and diagnostics, and a self-cleaning heat exchanger that resists limescale. The Lambda Pro control automatically adjusts to gas quality for consistent performance.
Viessman 20kw: Cost of the Unit
Cost of the unit ranges from £650 for the Vitodens 050-W 20kW to £900 for higher-spec versions, representing strong value in the premium compact segment.
Cost with Installation
Cost with installation typically totals £1,800–£2,600, including Gas Safe labour, flue, and condensate pipework. Straightforward swaps are cheaper than full system upgrades.
Running Costs
Running costs for a 2–3 bedroom home usually fall between £750 and £1,050 per year, benefiting from high modulation and efficiency. The Viessmann 20kW boiler stands out for its low running costs because its precise output adjustment prevents wasteful cycling, delivering reliable savings over time.
Viessman 20kw: Which? and Trustpilot Ratings
Which? and Trustpilot ratings for Viessmann are consistently strong, with the brand earning 5/5 reliability and Best Buy recognition in Which? surveys. Trustpilot shows 4.3/5 from over 5,300 reviews, praising performance and quiet running.
Is the Viessmann 20kw Boiler Right for You?
The Viessmann 20kW boiler suits properties with modest heating and hot water needs. Here’s expert guidance to help you decide.
Choose the Viessmann 20kW boiler if…
- Your home is small to medium (1–2 bedrooms, 1 bathroom).
- You want premium efficiency and quiet operation in a compact unit.
- Smart app control and weather compensation appeal to you.
- You value long-term reliability over the lowest upfront price.
Don’t choose the Viessmann 20kW boiler if…
- Your property has multiple bathrooms or high hot water demand.
- Budget is very tight and you need a basic entry-level model.
- You require higher outputs for larger radiator systems.
Need a New Boiler Quote?
Ready for an efficient upgrade? Request a new boiler quote from Boilers 2 Go. Our experts will recommend the best options for your home with competitive pricing and no obligation.
FAQs
How Does the 20kW Model Compare to the 25kW or 29kW Versions?
The 20kW version is more efficient and cheaper for small homes but offers lower hot water flow rates than the 25kW or 29kW models.
Can the 20kW Boiler Be Converted to LPG?
Yes, Viessmann offers official LPG conversion kits for off-grid properties, maintaining high efficiency with minimal adjustments.
What Filter Is Recommended for Hard Water Areas?
A magnetic system filter (e.g., Adey MagnaClean) is strongly recommended to protect the Inox-Radial heat exchanger from limescale.
Does the Viessmann 20kW Support Solar Thermal Integration?
Yes, it can be paired with solar thermal cylinders via optional kits to preheat water and further reduce gas consumption.
How Long Does a Professional Installation Usually Take?
A straightforward swap typically takes 4–6 hours, while more complex installations with new pipework or flues may require a full day.
I’m Penny North, a home energy heating expert. My mission is to demystify new boilers and complex heating systems to help you achieve a warm, cosy home with lower energy bills and a smaller environmental footprint.