Worcester Bosch Greenstar 25i Combi Boiler Review

The Worcester 25i is now Worcester Bosch’s flagship boiler range – and a pretty impressive range it is too. It builds on the success of their ‘Junior’ range which the ‘Greenstar’ range has now replaced. Worcester Bosch’s pedigree is legendary, they are every heating engineers ‘go-to’ brand and in this review we are going to:
  • Talk prices of Worcester’s 25i
  • Review specification
  • Discuss alternatives to the Worcester Bosch Greenstar range
  • Review & conclude with what’s best for you  
Lets jump straight in

Worcester Bosch 25i Price & Installation Cost

The question on most people’s lips is how much are Worcester’s 25i’s? It’s the elephant in the room so we may aswell kick things off here.

Boiler Only Cost

The answer is, a Worcester Bosch 25i costs £950-£1000, depending on the merchant. They are a ‘sought after’ premium boiler brand and will be up there in terms of price with Valliant and Veissman and Ideal. But that £950 is just for the boiler, you may also require: Flues – the flues job is to remove the toxic fumes from the boiler and vent these outside. The flue is the cylindrical pipe that comes off from the boiler unit and heads outside either through the wall or roof. Flues from Worcester cost around £150-£200 and flue extensions cost £55 each.  Controls – you’ve probably guessed the job of the controls but these could come as an added extra so factor this in. 

Boiler Cost & Installation

So just how much is it to install a Worcester Bosch Greenstar 25i? Well the good news is they are pretty much every engineer’s favorite boiler and tens of thousands of Worcesters get installed each year in the UK.  The reason I mention that is because engineers charge for their time. The quicker they can get someone done with little complexity the better. Or not better but ‘cheaper’ I should say.  A general rule of thumb with boilers is installation costs are the same as the boiler cost. However we decided to conduct a little ‘market research’ and got three quotes from [Gas Safe] local installers across the U.K. The brief was simple, we wanted a price JUST for the installation of our brand new Worcester 25i.  All the quotes were actually fairly close and when we averaged these quotes and added in the quotes we obtained online, the figure was £1250. So the total costs to buy and install a Worcester 25i was £2,200. But that was the average we found cheaper online – read below and grab a bargain.

The Cheapest Quote to Install A Worcester 25i Boiler

This was hands down from the online boiler comparison site Heatable. They are a breath of fresh air if you ask us. They are a new breed of ‘online boiler companies’ offering FIXED prices, on screen, in 60 seconds including installation, for Worcester’s 25i’s [infact all ranges of Worcester Bosch boilers].  Just click a few multiple choice questions to get a fixed price deal on a brand new boiler, all without giving out any personal information and then get a price instantly in front of you. No emails, no phone calls, no faffing about all with next day nationwide installation and finance available. Try them here. We did and this was the deal they offer on the 30kW [so bigger output] Worcester Bosch 25i
Sure they are the cheapest and to be honest price was the biggest determining factor BUT when you have a boiler installed with them, because they work so closely with Worcester Bosch they have actually become an ‘approved installer’, meaning you then get a 10 year warranty from Worcester themselves. From that point on it was an absolute no brainer… Included in that fixed quotation were ‘extras’ – these included:
  • A system clean to get rid of the sludge that has built up over the years in the rads.
  • A magnetic system filter that will trap any debris before it could hit the boiler and have a chance to damage it.
  • A complete system rebalance
  • Wireless heating controls!
They make it very straightforward and easy to compare one boiler to another and Heatable’s strap line is:  ‘’the prices you see onscreen are fixed including installation, VAT and will not change.” We like this! 

How to size your Combi Boiler?

Sizing a combi boiler is important as under spec’ing a boiler will mean it wont keep up with your hot water demand and could result in cold showers – yikes! The Worcester 25i is designed specifically for up to 3 bedroom properties that have a low heating and hot water demand. If you aren’t sure if that includes you then check.  The best way to find out is by using this online boiler size calculator. The Worcester 25i’s are usually installed into 2 bedroom properties with only 1 shower. So here we are talking about 2 bedroom flats or apartments or terraced two bedroom houses.  If you have more than 3 bedrooms, more than 10 radiators or more than one shower – you will likely require something bigger than the Worcester 25i. The next boiler up in spec from the 25i is the Worcester 30l. If that isn’t enough you can jump up again to a bigger boiler. Worcester has a fantastic range for all properties types and sizes so they have you covered.  Remember however, the Worcester 25i comes in two outputs: a 25kW [as the 25i name suggests] BUT also a 30kW.  If you are still struggling or just want a second opinion, fill out this simple online boiler sizing guide and it will tell you in plain terms which boiler is best suited for your home in just a few seconds. 

Better Hot Water Output

The current Worcester 25i, the ‘Greenstar 25i’ replaces the ‘Junior 24l’ which as the name suggests was only 24kW.  Worcester have decided to give the new range of 25i’s slightly more punch with an extra 1kW of output. It doesn’t sound alot; but it does increase water output to its current spec of 10.2 litres per min. 

25i Display Panel

The 25i now has a far better display panel with increased functionality. Users can, for example, change the water and heating temperature from the display panel and it’s now much more intuitive.  The big draw back with the Junior 24l was the lack of functionality making even simple tasks a bit difficult. The Junior 24l just wasn’t very intuitive.  Thankfully with the 25i that has all been replaced with a sleek functional design.  Plus if you ever have a boiler problem, the ‘fault code’ which corresponds to the relevant error, will be displayed on the display panel meaning an engineer can walk in and see the issue straight away. 


The 25i has something called a CondenseSure Siphon which stops the condensate pipe from freezing. This sounds simple but it wreaks havoc every winter for thousands of people. It’s actually one of the most common causes for engineers’ call outs. This means you will have far less problems over winter and one less reason for any costly call outs.

Boiler Servicing

Engineers used to report that the Junior 24l was difficult to service as it could be difficult to get at all the parts.  This is something with the new 25i’s that Worcester have addressed. They have made it easy to access all the parts within the boiler making servicing easier and less time consuming – meaning cheaper to service and also quicker to install. 

Worcester 25i Boiler Controls 

One really popular WIFI enabled ‘smart’ heating control is called the ‘Worcester Wave’. Using their ‘Wave’ app you can set and change temperature controls along with all the timings.  It costs extra but could be well worth it if controlling everything from your smartphone sounds up your street.  However as standard the 25i heating controls are exemplary and in true Worcester Bosch fashion are extremely robust. 

The Worcester 25i & The 25SI Compact

Both have 25 in their name, so what’s the difference? 

The Worcester 25i Compact Combi Boiler

As the name suggests, this is Worcester’s 25kW boiler that is compact enough to fit into a kitchen cupboard. The 25SI Compact is slightly smaller than the Worcester 25i. The 25SI Compact has been designed with space saving in mind. [We did say Worcester Bosch has a wide range!] 

Worcester 25SI Compact Cost

The 25SI Compact will cost you roughly £50-£95 more than the 25i. Whether this is worth it or not is completely dependent on you ‘the homeowner’. It could depend on where you are going to house the boiler. Most people would argue yes, it is worth it, if they want to hide the boiler away in a standard kitchen cupboard.  If the boiler is going under the stairs for instance or maybe in the bathroom, size is probably less of an issue. 

Which Is The Best Worcester Bosch 25 Boiler?

If you are short on space and trying to hide it away in a kitchen cupboard then the ‘25SI Compact’ is the one for you. If space isn’t an issue then the 25i is the best choice. 

Alternatives to the Worcester 25i?

As you would expect there are quite a few, as most manufacturers make a 25kW [or near enough] boiler but the problem is, for the price, not all are up to scratch when compared directly to the Worcester.   You really ought to rate a boiler with the following criteria:
  • Price
  • Warranty
  • Quality & Robustness
Price is simple, as if it’s too expensive and you can’t afford it, what’s the point in even reviewing it.  Warranty because as the saying goes ‘‘a boiler is only as good as its warranty’’.  Then lastly quality, because you don’t want the thing breaking down each winter.  So who else offers what and at what prices? Take Ideal for instance; Ideal makes the ‘Ideal Logic Plus 24’ and the ‘Ideal Vogue 26’, so a direct competitor to the Worcester 25i.  You’ll pay about 5-10% less for the Logic Plus 24 than you would for the equivalent Worcester 25i and you’ll get a respectable 7 year warranty with it from Ideal too. Really not to be sniffed at. Price wise on the Vogue 26 you will pay about the same as you would for a Worcester and get a 7+ year warranty, again like you would with the Worcester – so not really much to write home about.  Compare the two 30kW boilers below, there’s only £60 in it!   
To be honest it’s the same with other brands too, either they are cheaper because they have poor build quality or they are cheaper because they have a tiny warranty. And a short warranty, in effect, is the manufacturer saying even they don’t stand behind their product for long. So if they don’t, you shouldn’t either.  The Best Boiler Brands are:
  • Worcester
  • Viessmann
  • Ideal
  • Baxi
The best way to compare boilers and prices is by using this online boiler comparison site. After a few multiple choice, clickable questions you can see the best boiler for your home with the price – which is FIXED […and that includes installation!].

Worcester Bosch 25i Conclusion [Are they worth it?]  

Short answer: Yes, hands down. Best boiler on the market for the price when you use an online boiler installer like Heatable. Long answer: When you can get a Worcester 25i for basically about the money as the: Viessmann Vitoden 050-W 29kW Ideal Logic Plus 24  Baxi Duo tec 24 – 24kW/30kW But ALSO get up to a 10 year warranty the Worcester 25i is the clear winner. Check out the best deals on a brand new Worcester Bosch 25i’s here.