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Worcester Bosch Greenstar 30i vs Worcester Bosch Greenstar 30Si Compact Combi Boiler – Review

Welcome to another edition of the battle of the boilers. In today’s contest, we have two of the most popular combination (also known as ‘combi’) boilers on offer from Worcester Bosch; the Worcester Bosch Greenstar 30i, and its smaller twin the Worcester Bosch Greenstar 30Si.

If you’re struggling to decide between boilers, there are a few factors you’ll need to consider. These factors include the price, size, control and energy efficiency. As a general rule of thumb, combi boilers are more suitable for small to mid-sized properties with 1-3 bedrooms and 1-2 bathrooms. Combi boilers aren’t able to cope with the high water demand required by multiple bathrooms. Before the battle begins, let’s take a closer look into this UK-loved manufacturer.

Worcester Bosch is a UK-born and bred domestic heating and hot water products manufacturer. As a brand, Worcester Bosch has a high satisfaction score among customers and engineers, which is strengthened further by over five decades of experience. Worcester Bosch has a heavy focus on high quality and energy-saving products.

Are you ready to take a closer at the boilers?
The table below shows the basic stats for each boiler model:

 Worcester Bosch Greenstar 30iWorcester Bosch Greenstar 30Si Compact
Other outputs available2525
ErP rating (energy efficiency)A (93%)A (94%)
Size (HxWxD in mm)710x400x330690x390x280
Heating output (kW)2424
Hot water output (kW)3030
Flow rate (litres/min)12.312.3
Standard warranty (years)5 (extended warranties available)5 (extended warranties available)


As both boilers are built in a very similar fashion, each of their control panels has the same layout and controls. For a combi boiler, the standard controls you can expect are a switch to turn the boiler on or off, the ability to increase/decrease output, as well as a display, which will show you an error code should the boiler encounter an issue.

To have more control of your boiler, it’s important to have heating controls installed in your home, whether they’re mechanical or digital. Mechanical controls are your most basic form of boiler control, which is usually a small dial installed on a wall which can be turned to control your temperature settings. Digital controls will allow you to create heating schedules across 7 days and control your boiler.

To take full advantage of your combination boiler, Boiler Plus was introduced in 2018 to ensure that all homes have time and temperature controls installed at the minimum for their boiler. The aim of Boiler Plus is to improve the energy efficiency of homes nationwide by installing high energy-efficiency rated boilers with the appropriate controls.

For combination boilers, there are four additional requirements that will need to be met by the homeowner to be compliant with Boiler Plus. The requirements are as follows:

  • Weather compensation – Water temperature is altered from the boiler based on the outdoor temperature.
  • Load compensation – Water temperature is altered from the boiler based on the current room temperature.
  • Smart control – A type of control that provides automation and optimisation for your boiler
  • PFGHRD (Passive Flue Gas Heat Recovery Device)

If you’d like an upgrade over the conventional mechanical or digital thermostat, you could also look into smart thermostat options. Worcester Bosch offers a smart thermostat called the Worcester Wave, which is their entry into the smart thermostat marketing. With the Wave, you can control and monitor your central heating system from your smartphone, tablet or laptop, whether you’re at home or away. If you’d like to venture away from the Wave and take a look at other smart thermostat options, the Nest Learning Thermostat offers an abundance of additional features, including self-learning from your heating routine and the times you’re home or away.

Each Hometree boiler installation comes with a Honeywell T6 Lyric smart thermostat at no additional cost

In this category, it’s almost impossible to compare each of the boiler’s control panels due to their simple and easy-to-use layouts, as well as how similar they are to each other. Since both boilers are so similar, each boiler gets a point – making it a draw at 1-1.


When comparing the two boilers, the Worcester Bosch Greenstar 30Si is the smaller and more compact version of the 30i boiler. The 30i measures 710mm x 400mm x 330mm, and the 30Si comes in at 690mm x 390mm x 280mm. If space is an issue, the 30Si is easily the best choice since it can fit into any standard-size kitchen cupboard. The 30i, however, isn’t suitable for kitchen cupboards and is probably better off in a utility cupboard or on the wall if you can find a space in your kitchen. It’s a point to the 30Si, 2-1.

Energy Efficiency

Due to advances in technology and innovation around energy products, the efficiency of products such as boilers has dramatically improved. The energy efficiency rating of the Worcester 30i is a whopping 93%, while the 30Si has the leg up at 94%. Both of these boilers offer an A-grade for energy efficiency, which means you can expect to not only reduce your carbon footprint but also make a saving on your energy bills.

Who’s behind the boiler energy ratings? The ErP (Energy-related Product) directive, which tests and improves new energy products before they’d sold and installed by engineers. The ErP directive was introduced in 2015 and has the power to stop the sale of certain products if they do not pass specific criteria. The ErP’s primary goal is to reduce the amount of carbon emissions produced by homes and to help you save money on energy.

Seeing as both boilers have been rated an A-grade overall, and the difference between the boilers’ energy efficiency is 1%, it’s an incredibly close contest. The Worcester 30Si gains a point and remains in the lead due to its slightly higher energy efficiency. Will the Worcester Bosch Greenstar 30i catch up? Let’s find out in the next round. 3 – 1 to the 30Si.


The standard warranty for each Worcester Bosch Greenstar boiler is 5 years. If you’d like to extend your warranty, you can extend your warranty by a further 5 years by having your boiler installed by a Worcester Accredited Installer. At Hometree, we offer extended 5-year warranties, for free, with each of our boilers, including our range of Worcester Bosch products. We also offer 10-year warranties for an extra charge.

Since both boilers offer the same warranty, it’s a point to each boiler. The 30Si remains in the lead and it looks like we already have a winner! Let’s see how the 30i performs in the next round. It’s 4-2 to the 30Si.


Worcester Bosch as a manufacturer of heating products has received Which? Best Buy Awards for a total of 7 years running. The awards were received for their high-quality combination gas boilers. In addition to Best Buy Awards, they have also received high customer satisfaction and engineer recommendation scores for 6 years running.

Given the multitude of awards for all Worcester Bosch gas boilers, each boiler earns a point in this category. We have a winner!

The verdict

The Worcester Bosch Greenstar 30Si wins the latest edition of the battle of boilers with a score of 5-3!

To conclude this edition of ‘battle of the boilers’, the 30Si is a clear favourite for households that are looking for a compact boiler that meets their hot water and heating requirements. The 30i is larger in size and only slightly (by 1%) less efficient than the 30Si. Both boilers share a lot of similar characteristics, including central heating output and flow rate, and the same control panel layout.

To get your price for the Worcester Bosch Greenstar 30Si and 30i, all you have to do is answer a few simple questions through our website. We’ll be able to give you a free quote for the boiler, including installation and a free smart thermostat.

 Worcester Bosch Greenstar 30iWorcester Bosch Greenstar 30Si Compact
Energy Efficiency01

Which? Boiler Review The consumer group Which? review each boiler on the market to find the most (and least) reliable boilers according to a survey completed by thousands of boiler owners. In each review, Which? supply a brand score percentage and star ratings for each category. Take a look at the Worcester Bosch Greenstar 30i and 30Si brand rating below:

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