Are you looking for a compact Worcester Bosch combi boiler for your small to medium sized Edinburgh property?

The Worcester Bosch Greenstar 25si compact and 30si are a good choice – but which one do you pick?

You’re in luck, as many of my customers have the same dilemma, prompting me to compare the two in this very special blog post.

So, read on to find out all you need to know about the Greenstar 25si and 30si…


These are one of my favourite models of Worcester Bosch boilers, and I’m going to tell you why. Because they’re so compact, you can fit them almost anywhere – and they’re also incredibly simple to install.

They’re slightly cheaper then Worcester Bosch‘s cdi range, but they’re still fantastic quality and come with a 9-year no quibble guarantee (which I’ll tell you more about below).

Output and flow rate

Both the 25si and 30si supply an output of 24kw to your central heating, which will comfortably heat a small to medium-sized property. However, the main deciding factor between these two boilers is the hot water output.

The hot water output on the 25si supplies 10.2 litres of hot water per minute, which is ideal for running a shower – however, this is NOT suitable if you have a bath as it will be slow to fill. In comparison, the 30si provides a hot water output of 12.3 litres, giving you just that little bit extra oomph to comfortably run a bath or shower.


Both of these models are compact, so there’ll ideal if you need all the space you can get in your small flat or house. The 25si and 30si take up minimal space and will easily fit in your kitchen cupboard or Edinburgh press.

TIP: If a compact model isn’t an absolute must for your home, I’d recommend opting for the 25i and 30i instead INSERT LINK TO 25i AND 30i COMPARISON REVIEW).


Worcester Bosch the absolute best no-quibble boiler guarantee on the market. I like to look out for my customers, which is why I always recommend the Worcester Bosch guarantee over any other.

The good news is that both Greenstar si models come with 9year guarantees* when fitted with Worcester Greenstar filter and comfort controls which are are covered for 9 years that will have you covered in all eventualities.

Although you may find other boiler companies offering slightly longer guarantees for very similar models, you’ll find there’s often a catch in the small print, or extra credit card charges before they’ll even agree to a call-out.

At a Glance

Below, I’ve put together a quick summary of the tech specs you need to know for the 25si and 30si:


  • Heating output: 24kw
  • Hot water output: 25kw
  • Ideal for: Small to medium-sized properties with one shower room (slow to fill a bath)
  • ERP rating: A, 93% efficiency
  • Guarantee: 9 years*


  • Heating output: 24kw
  • Hot water output: 30kw
  • Ideal for: Small to medium-sized properties with one bathroom
  • ERP rating: A, 93% efficiency
  • Guarantee: 9 years*


If you’re in the market for a compact Worcester Bosch boiler for your small to medium-sized Edinburgh property, the Greenstar 25si and 30si are a great choice. The above comparison blog tells you all you need to know, but the main deciding factor here is the hot water output.

Depending on whether you need to run a bath and shower, or just a shower, you should either opt for the 30si or 25si respectively. And both are super compact, so they’ll happily fit in your kitchen cupboard or Edinburgh press!

Finally, the 9-year no quibble guarantee* ensures you’re covered on the off-chance anything should go wrong.

Which Greenstar si model will you choose?

*9 year guarantee subject to boiler being serviced annually by a Gas Safe Registered engineer.