The Worcester Bosch Greenstar 4000 and 8000 are the brand's two main residential combi ranges. Both are excellent boilers — but they have different value propositions. Here's how to decide between them.
Efficiency
Greenstar 4000: up to 94% ErP. Greenstar 8000: up to 95.3% ErP. The difference is approximately 1–1.3 percentage points — translating to perhaps £12–£15/year on a typical gas bill. Meaningful over 12 years (£150–£180), but not dramatic.
Warranty
This is the biggest difference. Greenstar 4000: up to 8 years with Worcester Bosch Accredited Installer. Greenstar 8000: up to 12 years. Over a 15-year boiler lifespan, 4 extra years of warranty cover is genuinely significant. A single heat exchanger failure under warranty saves £400–£600.
Build quality
The 8000 uses a stainless steel heat exchanger. The 4000 uses a proven aluminium heat exchanger. Both are durable — but stainless steel is generally considered the premium choice for longevity.
Hot water performance
The 8000 offers slightly higher DHW flow rates at equivalent outputs — useful for homes with two bathrooms.
Price difference
The 8000 typically costs £200–£350 more to supply and install than the 4000.
Our verdict
For most homeowners: the Greenstar 8000. The 4-year extra warranty and stainless steel heat exchanger are worth the premium over a 12+ year boiler lifespan. The 4000 is excellent value for budget-conscious buyers who want the Worcester Bosch name without the top price.