Dilemmas, dilemmas… they can happen to the best of us.

Are you having one of your own about whether to choose the Greenstar Highflow 440cdi or 550cdi for your large Edinburgh home?

Don’t worry, many of my customers have the same trouble, which is why I thought I’d put together this helpful blog comparing the two.

So, without further ado, let’s take a closer look at the Greenstar Highflow 440cdi and 550cdi…


The Greenstar Highflow 440cdi and 550cdi both offer fantastic flow rates and capacity to comfortably heat your large home. You’ll ideally be looking for one of these if you have multiple bathrooms and don’t want to have to worry about running out of hot water.

I personally have had the Greenstar Highflow 440cdi installed in my own home for eight years now, and it’s never missed a beat – so these models are also ultra reliable.

But what’s the real difference between the two?

Output and flow rate

With a heating output of 29.2kw and a hot water output of 29.5kw (supplying 20 litres of water per minute) you’ll find the 440cdi can take just about everything you throw at it.

With the 550cdi, there’s not a huge difference in the heating output. However, if you want the ultimate hot water from a combi boiler (for instance, if a few people are likely to be using it at once), this should definitely be your choice, as it has a hot water output of 41.1kw and can supply an amazing 25 litres per minute of hot water.

TIP: Before an engineer installs the 550cdi, they should first check your incoming water pressure to ensure you’re definitely going to get the benefit – if not, you may be better off with the 440cdi.


Both of these boilers are what’s known as floor standing models, and they tend to take up quite a bit of space – picture them as around the size of a washing machine.

Because of their size, they won’t fit in most cupboards, and they cannot be wall hung – but they’d be probably be ideal for fitting in a utility room, basement or garage.


Although Worcester Bosch boilers are incredibly reliable, you’ll still want to ensure your investment is protected should anything go wrong, which is why you need a good guarantee.

And great news – all Worcester Bosch cdi models are subject to what is probably the best no quibble 10-year boiler guarantee* on the market right now when fitted with Worcester Bosch Greenstar filter and comfort controls – which are also covered for 10 years. It’s actually one of the reasons I recommend this particular brand to all my customers.

It’s true that you may find other boiler companies offering slightly longer guarantees for very similar spec models, but you’ll often find there’s 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 summary of the important info and tech specs for each boiler:


  • Heating output: 29.2kw
  • Hot water output: 29.5kw
  • Ideal for: Large homes with multiple bathrooms
  • ERP rating: A, 93% efficiency
  • Guarantee: 10 years*


  • Heating output: 30.6kw
  • Hot water output: 41.1kw
  • Ideal for: Large homes with multiple bathrooms
  • ERP rating: A, 92% efficiency
  • Guarantee: 10 years*


Confused about which model of Greenstar Highflow you need for your home? Many of my customers are the same, which is why I’ve come up with the above run-down of everything you need to know about the Greenstar Highflow 440cdi and 550cdi.

Both offer fantastic flow rates and can comfortably heat your large home, however if you want the ultimate hot water from a combi boiler (for instance, if you often have multiple people using the hot water simultaneously), I’d recommend the 550cdi.

My tip here is to always get your engineer to check your water pressure before installing the 550cdi, as if it is low, you may not get the extra benefit. In which case, you should probably opt for the 440cdi instead.

And finally, both of these boilers come with a fantastic 10-year no quibble guarantee,*so you’ll be covered whatever happens.

Have you decided which Greenstar Highflow model you need yet?

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