Having plenty of choice can never be a bad thing… can it?

But when you’re faced with a plethora of Greenstars, highflows, i, si, cdi, compact and classic… sometimes things can get a bit confusing when choosing the right boiler for your home.

That’s precisely why I’m welcoming you to the first in a very special series of blogs, where I’m not only going to be reviewing specific models of Worcester Bosch and Vaillant boilers – I’m also going to be pitting some of them against each other.

Basically, I’m going to be doing all the hard work, so you don’t have to!

So, let’s start by taking a closer look at the most recent additions to the Worcester Bosch range; the Greenstar 25i and 30i combi boiler.


So, Worcester Bosch recently waved goodbye to its bestselling Greenstar Junior boilers, and rolled out these latest, new and improved, energy efficient models.

And you should be particularly happy about that, as now you can look forward to the same quality you’ve come to expect from Worcester Bosch, only with better flow rates than ever before. They’re also very easy and straightforward to fit.

Plus, because Greenstar i boilers fall in-line with the new standards set by the ERP directive (kicking into place on the 26th September), you’ll also save money on your energy bills. What’s not to love?

Output and flow rate

I like to think of the Greenstar i as the Vauxhall Corsa of boilers. The 25i is the city car version; small, and very economical and does all the basics you need it to. The 30i on the other hand, has a bit more punch to it – it’s good for going down the bypass (although still not exactly a motorway cruiser).

What I’m trying to say is, these boilers are designed to best suit small to medium-size properties, and the hot water output is really the deciding factor with these boilers.

The 25i will quite easily heat your one or two-bedroom home and run your shower, but at only 10.2 litres of hot water per minute, it’s not ideal if you want to run a bath. The 30i is your bath option, and supplies 12.3 litres of hot water per minute, whilst actually being just that tiny bit more energy efficient, too.


The 25i and 30i boilers are 330mm deep, so not exactly the smallest option available – you’ll find they won’t fit inside a standard kitchen cupboard or Edinburgh press.

If you don’t have any other options, and absolutely must fit your boiler in a small cupboard, I’d recommend fitting one of Worcester Bosch’s compact models, as an alternative.


Worcester Bosch has one of the best no-quibble boiler guarantees on the market, which is one of the reasons I recommend them to all my customers. And you’ll be happy to learn that both Greenstar i models come with 8-year guarantees.*

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, you’ll find a run-down of the tech specs for each boiler:

The 25i

  • Heating output: 24kw
  • Hot water output: 25kw
  • Ideal for: Small to medium-sized properties with one shower room (not ideal for baths).
  • ERP rating: A, 93% efficiency
  • Guarantee: 8 years*

The 30i

  • Heating output: 24kw
  • Hot water output: 30kw
  • Ideal for: Small to medium-sized properties with one bathroom (will easily run a bath)
  • ERP rating: A ,93% efficiency
  • Guarantee: 8 years*


There are so many different models of boilers on the market, which can make things confusing when you don’t know which to choose. That’s why I’m going to make it just that bit easier, by comparing popular Worcester Bosch and Vaillant models.

Worcester Bosch’s new Greenstar i combi boiler range was recently introduced to meet the new standards set by the ERP directive, and because of that they’re super energy efficient and provide much better flow rates than the old Greenstar Juniors.

The 25i will easily heat your one to two-bedroom home, and will supply hot water to one shower room at 10.2 litres per minute – however, if you want to run a bath, the 30i is your best bet.

Have you decided which Greenstar i is right for you?

* 8 year guarantee is when installed by a Worcester accredited installer and fitted with a Worcester Greenstar central filter