2021 Boiler Comparison: Worcester Greenstar 30 CDi Classic System vs. 30i System

Are you looking at both the Worcester Greenstar 30 CDi Classic System and the Worcester 30i, and aren’t sure which boiler is right for you?

This review has all the information you need to make an informed decision.

Worcester Greenstar 30 CDi Classic System

What Is a System Boiler?

A ‘system boiler‘ is a type of boiler that comes with a separate cylinder for storing hot water. Unlike their older-fashioned conventional counterparts, system boilers draw water directly from the mains instead of relying on a feed tank. That said, system boilers are more cumbersome than the popular combis, which don’t need storage cylinders and only supply heat and water on demand.

If your existing heating setup relies on a hot water cylinder, you can swap your old system boiler for a new one. Alternatively, you can get a combi and free up some space, just note that combis may not provide sufficient heat and hot water if your household has got excessive water demand. For instance, if you ever run 2 showers at once while the heating system is on, a combi boiler may not suffice — you’re better off sticking to the system boiler.

If you have a cold feed, you’ll need a new conventional boiler (aka regular, heat only, or traditional boiler).

Check our guide to the different types of boilers here if you’re unsure which boiler type you have.

Is the Worcester 30 CDi Classic Big Enough for My House?

The Worcester Greenstar 30 CDi is suitable for reasonably large properties, up to 4-5 bedrooms. Just keep in mind that you’ll need a large heating run and up to 15 radiators for a home of this size.

That said, calculating a boiler’s size with precision relies on more variables than just the home’s size. To ensure the Worcester Bosch 30 CDi is the right boiler for your house, you can use this boiler size calculator. All you need to do is answer a few multiple choices questions about your property, and you’ll get the most suitable boiler (along with a fixed price) on your screen in minutes.

Worcester Greenstar 30i vs. Greenstar 30 Cdi

Both the CDi Classic and the I System range from Worcester are system boilers. Both would be a direct replacement for your current system boiler.

The only difference between the 2 ranges is the appliances’ dimensions.

If you’re looking to fit your boiler into a tight area — such as a kitchen cupboard — you’ll need the Worcester Greenstar 30i System; NOT the 30 CDi Classic.

HEATABLE Worcester Bosch Greenstar i 30kW

The Greenstar 30 CDi Classic measures 760 x 440 x 360, so it’s best to wall-hang them in large installation areas, like a garage or airing cupboard.

The Worcester Greenstar 30i System, on the other hand, is much smaller at 690 x 390 x 280, so it’s suitable for compact installation spaces.

Note that if you want to install your replacement boiler in a NEW place, like a kitchen cupboard, you’ll have to pay a bit extra to relocate all the infrastructure. Depending on where you’re moving your boiler from, you could be looking at £150-350 on top of the regular installation costs.

You can compare prices for moving your boiler, and the difference in price between the CDi Classic and the 30i system, here.


We regularly bang on about the importance of boiler warranties.

And for good reason.

There are lots of brands offering boiler models with a measly 1-2 year warranty. In our opinion, these short warranties don’t give you the confidence to make a purchase, even if the appliance you’re buying is cheaper than a typical Worcester.

Normally, installing a premium-brand boiler, like the Greenstar 30CDi, should set you back in excess of £2,600. You could reduce this cost to £2,300 or less with a boiler with a short warranty, but I certainly wouldn’t take that risk. Because if your new, cheap boiler breaks after the 2 year warranty is up, you’ll be footing that bill all over again.

We prefer models and manufacturers that offer warranties in excess of 5-years. Both the Worcester Greenstar 30i and the 30 CDi come with a 10-year warranty when you purchase through a company like Heatable.

Worcester’s warranties are usually shorter, around the 8-year mark. But Heatable have a solid business relationship with Worcester Bosch, so they get favourable warranties and prices to match.

Heatable boiler calculator

Worcester 30 CDi Installation Costs

As we’ve already mentioned, you should expect to pay in the region of £2,600 to get a 30 CDi fitted on your property.

Like any installation, the price will vary depending on the details. For instance, if you need the flue or boiler in a new location, the cost will increase slightly.

We used this this price calculator, and got a figure of £2,610 for a basic installation, with a 10-year warranty for both the Greenstar 30i Compact and the 30 CDi System boilers.

Worcester Bosch Reviews

It’s not always easy to find specific product reviews for boilers.

But, before you purchase a new boiler, you’ll find a range of different reviews online from customers that have bought from the brand in the past. That’s going to give you an idea about everything from product quality, warranty, and even customer support.

You can check out Worcester Bosch reviews on Trust Pilot here – they’re currently rated as “Excellent” from more than 24,000 user opinions (at the time of writing).

Worcester Bosch boilers - Trustpilot review

They’ve also received the Which? Best Buy award now for the 9th year in a row.

Interesting Features 

Frost Protection

One important feature integrated into the Worcester boiler range is the Condensesure Siphon.

Put simply, the Condensesure Siphon is a feature designed to stop boilers freezing up during the cold months of the year. Not only will it protect your boiler, it’s also going to shield you from expensive repair bills.

It’s tested above and beyond conditions we’re likely to experience in the UK. The Condensesure Siphon will protect your boiler at down to -15°C for up to 48 hours!

Energy Savings

We all like free cash.

A report by the Energy Saving Trust found that newer, A-rated boilers like the Greenstar 30i or the 30 CDi could save homeowners up to £305 per year on their energy bills.


These savings are possible thanks to a combination of eco-friendly, efficient boiler components. In the case of most Worcester boilers, part of that energy saving comes from the pump, which uses a ridiculously low amount of energy.

Should You Buy the Worcester 30 CDi Classic System?

The Classic 30 CDi isn’t the cheapest boiler on the market, but it offers one of the longest warranties from a leading brand. We give it a thumbs up.

The only instance we’d be avoiding the Classic System is if you’re aiming to hide your boiler away in a kitchen cupboard. If this is the case, the Greenstar 30i System is a much more suitable option.

You can get and compare prices for both models here.

What’s Next?

Thanks for reading our 30 CDi Classic System review. Hopefully, it gives you enough information to make a decision on which boiler is going to be your next.

Got questions? Drop us a line via our contact form, and we’ll get back to you as soon as possible.

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