Vaillant aroTHERM plus vs Worcester Bosch Compress 5800i AW: Which Should You Choose?

Case study · heat pump comparison

The Vaillant aroTHERM plus and the Worcester Bosch Compress 5800i AW are two of the most direct rivals on our hub. Both are monobloc, both use the natural refrigerant R290, and both can reach 75°C, which is useful when replacing a boiler in an existing home. This guide compares them on output, noise, efficiency rating and installation. For each full range, see our Vaillant and Worcester Bosch pages, or go back to the heat pump hub.

Vaillant

aroTHERM plus

3.5 to 12kW

Type: R290 monobloc, up to 75°C

Best for: Small to large homes

Worcester Bosch

Compress 5800i AW

4, 5 and 7kW

Type: R290 monobloc, up to 75°C

Best for: Small to medium homes where noise matters

What they have in common

Both heat pumps keep the refrigerant sealed inside the outdoor unit. Vaillant describes the aroTHERM plus as using monobloc technology with a hermetically sealed refrigerant circuit, and Worcester Bosch describes the Compress 5800i AW as F-Gas free fitting with a monobloc design. That means only heating water runs between the outdoor unit and your home, and the installer doesn’t need to handle refrigerant.

Both use R290, also known as propane, a natural refrigerant with a very low global warming potential. Both are rated for flow temperatures up to 75°C, and both hold Quiet Mark certification. If you’re new to these terms, our guide to monobloc vs split heat pumps explains the difference.

Output range and home size

This is where they separate. The aroTHERM plus comes in 3.5, 5, 7, 10 and 12kW, so the same model can cover a small, well insulated home or a large detached house. The Compress 5800i AW is listed by Worcester Bosch in 4, 5 and 7kW, which covers many small and medium homes. For larger homes, Worcester Bosch lists its Compress 7001i AW instead.

Getting the size right matters more than choosing the bigger unit. Your installer should base it on a room-by-room heat loss calculation, because a heat pump well matched to your home runs more efficiently than one that’s oversized.

Noise

Noise is a common concern with any outdoor unit. Worcester Bosch calls the Compress 5800i AW its quietest heat pump ever, with an integrated diffuser, and it is Quiet Mark certified. Vaillant’s aroTHERM plus holds Quiet Mark on its 3.5, 5, 7 and 12kW models, with the 10kW model excluded. In practice both are a strong choice where the unit sits close to a boundary, but your installer should still check the exact position.

Efficiency rating and controls

Vaillant gives the aroTHERM plus an A+++ energy efficiency class. Worcester Bosch lists the Compress 5800i AW as A+++ for heating at 35°C and A++ at 55°C. Real-world efficiency depends far more on the design and flow temperature than on the label, so ask your installer for a performance estimate for your home.

Worcester Bosch highlights remote monitoring through its HomeCom Easy app for the Compress 5800i AW. If app control matters to you, ask your installer to show you the controls for whichever model they recommend.

Both heat pumps heat your hot water through a cylinder rather than instantly like a combi boiler. Your installer should size the cylinder to your household and tell you which one they plan to pair with the heat pump, as this affects how much indoor space you need.

Installation and guarantee

Both are straightforward for an experienced heat pump installer, since neither involves refrigerant work on site. Worcester Bosch points to rear-facing connectors for a quicker installation. Guarantee terms can depend on the installer and the parts fitted. Vaillant, for example, ties its extended guarantee to approved installers and registration with a Vaillant cylinder, so ask exactly what is included in your quote.

aroTHERM plus vs Compress 5800i AW compared

Which should you choose?

Choose the aroTHERM plus if:

• Your home needs more than 7kW
• You have a small, well insulated home that suits a 3.5kW unit
• Your installer is a Vaillant specialist

Choose the Compress 5800i AW if:

• Your heat loss falls within the 4 to 7kW range
• Quiet running is your top priority
• You like the idea of monitoring your system from an app
• Your installer is a Worcester Bosch specialist

Also weighing up Viessmann? Read Vaillant aroTHERM plus vs Viessmann Vitocal 250-A. Still deciding whether a heat pump is right for you? See heat pump vs gas boiler. You can also browse the Viessmann and Ideal ranges to see how other brands approach the same job, from compact units for small homes to larger outputs for detached houses.

Frequently asked questions

Which is quieter, the aroTHERM plus or the Compress 5800i AW?

Both are Quiet Mark certified, the aroTHERM plus on its 3.5, 5, 7 and 12kW models. Worcester Bosch calls the 5800i AW its quietest heat pump ever. Either is a good choice where noise matters, but ask your installer to check your unit’s position.

Can both work with existing radiators?

Both reach flow temperatures up to 75°C, which gives flexibility where radiators stay. The heat loss calculation decides whether any rooms need larger radiators so the heat pump can run at lower, more efficient temperatures.

What if my home needs more than 7kW?

The aroTHERM plus is available in 10 and 12kW. Within the Worcester Bosch range, the Compress 7001i AW is listed for larger homes. Your installer’s heat loss calculation will show the size you need.

Do both qualify for the Boiler Upgrade Scheme grant?

Vaillant confirms the aroTHERM plus is eligible. For any model, your installer checks eligibility and applies for you: £7,500 in England and Wales, or £9,000 for off-gas-grid homes replacing oil or LPG until March 2027. In Scotland, Home Energy Scotland grants apply. Our grant guide explains the process.