Vaillant vs Worcester Bosch heat pumps: which R290 monobloc wins?

Quick answer: Worcester Bosch wins this one on noise. Its Compress 5800i AW publishes 40 to 42 dB(A) sound power; Vaillant’s aroTHERM plus is 51 to 55 dB(A) in its own manual. On efficiency they’re close: at 55°C flow, Vaillant’s installer guide gives 3.06 to 3.39 for the 3.5 to 7kW sizes and Worcester’s MCS figures are 3.03 to 3.29. Both reach 75°C on R290.

We haven’t tested these units. This is based on published specifications, warranty terms and UK trade prices, all checked on 28 July 2026.

Two propane monoblocs, one big noise gap

The Vaillant aroTHERM plus has been the default British R290 heat pump for four years. It arrived early, it hits 75°C, and installers know it. Worcester Bosch came late with the Compress 5800i AW, and its specification sheet gives MCS SCOPs at 35, 45 and 55°C.

Vaillant publishes the same kind of curve. Its installer’s quick guide (March 2024) gives a SCOP for every size at 35, 40, 45, 50 and 55°C, though it doesn’t say which test basis it uses. On those figures the two are within about 0.2 of each other at every flow temperature. So efficiency won’t decide this. Noise will.

Head to head

The 40 dB(A) claim, and whether to believe it

Worcester’s specifier guide lists sound power to EN 12102 as 40 dB(A) for the 4kW and 42 dB(A) for the 5 and 7kW. That is the lowest published sound power figure of any mainstream UK air source heat pump we’ve checked, roughly ten decibels below the Vaillant. Ten decibels is heard as about half the loudness.

Is it real? It’s a manufacturer figure to a recognised standard, published in a document Worcester puts its own name on, so treat it as real until someone measures otherwise. What it buys you is planning headroom. Under the England permitted development rules that changed on 29 May 2025, your installer runs the MCS 020 a) sound calculator and has to show no more than 37 dB at 1 metre from the nearest neighbouring habitable room window or door. A unit that starts ten decibels lower gives you siting options a louder one doesn’t.

Vaillant’s own installation manual is clear: 51 dB(A) sound power for the 3.5 and 5kW, 53 dB(A) for the 7kW, rising to 54 and 55 dB(A) when the flow is at 55°C. Noise reduction mode pulls it down to 46 dB(A) at A-7/W35, at the cost of output. Worth knowing, because several UK trade listings advertise the aroTHERM plus at 44 dB(A) on the strength of its Quiet Mark accreditation. That figure does not appear in Vaillant’s own sound power table. Use the manual.

Efficiency at the temperatures you’ll run

Vaillant’s headline 5.03 is real, but it’s the 10kW at 35°C, and hardly any British retrofit runs at 35°C. At 55°C its installer guide gives 3.10, 3.06 and 3.39 for the 3.5, 5 and 7kW. Worcester’s 4, 5 and 7kW post 3.03, 3.28 and 3.29, on the MCS basis your grant paperwork runs on. Worcester is slightly ahead at 35 and 45°C; at 55°C it’s a tie. Vaillant doesn’t state its test basis, so gaps that small don’t mean much.

On Worcester’s own numbers, the 7kW falls from 4.54 at 35°C to 3.96 at 45°C and 3.29 at 55°C. That’s a 27% efficiency loss for a 20°C rise in flow temperature, and it’s typical. It’s also the single most useful thing a manufacturer can tell you, because your radiator sizing decides where on that curve you sit. If you want the SCOP-to-bills arithmetic, we’ve done it in COP explained.

Guarantees

Vaillant is 2 years as standard. myREWARDS Silver installers can offer 3, Gold, Platinum and Renewable Partners can offer up to 5, and 7 years is available only from Renewable Partners and Platinum members when the heat pump is fitted with a Vaillant hot water cylinder. Registration within 30 days, annual service, no exceptions.

Worcester Bosch doesn’t list heat pump guarantee lengths on its professional guarantee-lengths page, which covers gas, oil and air conditioning only when we checked on 28 July 2026. Trade listings and Worcester’s own 5800i marketing quote 7 years via an accredited installer on a 2-year base. Get the guarantee length written into your quote rather than assumed.

Which to buy

Take the Worcester Compress 5800i AW if the unit is going on a terrace, a semi with a close boundary, or anywhere a neighbour’s window is within a few metres. Its published noise advantage is large enough to change what’s possible. On efficiency it’s marginally ahead at 35 and 45°C and level at 55°C, so you give nothing up for the quiet.

Take the Vaillant aroTHERM plus if you want output above 7kW, or if your installer is a Vaillant Renewable Partner and will pair it with a Vaillant cylinder for the full 7 years. Worcester’s 5800i range stops at 7kW, so a bigger house means the Compress 7001i or another brand entirely. And the aroTHERM plus is 15 to 29kg lighter, which matters when it’s going on a wall bracket.

Where neither is right: a detached house with a 12kW heat loss. Neither of these specific models covers it. Look at the wider field in our brand comparison, and get the sizing settled first with our heat pump sizing guide or the cost calculator.

FAQs

Is the Worcester Bosch heat pump really quieter than the Vaillant?

On published EN 12102 sound power, yes, by about 10 dB(A). Both are measured to the same standard. Ask your installer to run the MCS sound calculator for your actual siting before you commit, because position and reflective surfaces move the result more than the unit’s rating does.

Does the aroTHERM plus really do SCOP 5.03?

Only the 10kW, and only at 35°C flow, on Vaillant’s installer guide. The 3.5, 5 and 7kW are rated 4.36 to 4.48 at 35°C, 3.65 to 3.91 at 45°C and 3.06 to 3.39 at 55°C, in line with other R290 monoblocs.

Do both qualify for the Boiler Upgrade Scheme?

Yes, if the model is MCS-listed and installed by an MCS-certified company. The standard grant is £7,500 in England and Wales. VAT on heat pumps is zero-rated until 31 March 2027.