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Glow Worm Ultimate 30C Boiler Review [And the Best Alternatives]

If you’re looking for a budget boiler, your online search may have led you to the Glow Worm brand. And, in the next 5 minutes, our Glow Worm Ultimate 30C boiler review will cover everything you need to know to decide if this boiler is right for you.

Glow worm 30C review

Glow Worm Ultimate Boiler Sizing

Before we get into specifics, you’ll need to determine what boiler size you need. We’ve already created a detailed guide on how to size up your boiler here.

For this review, though, we’ll focus on the most popular boiler model — the Glow Worm Ultimate 30C. This model is a 30kW combi boiler, which is powerful enough to serve the average-sized property in the UK (i.e. a 3-4 bedroom semi).

`That said, the boiler also comes in a 35 kW version, in case you have a larger home.

Glow Worm Ultimate 30C vs Worcester 30i

The biggest question we get asked when reviewing any boiler is whether to choose a Worcester Bosch model instead. Now, we’re not in the game of spending money for the sake of it, but Glow Worm are typically known as a budget brand. And low boiler prices tend to equate to one of two things:

  1. Low Quality
  2. Short Warranty

Now, let’s see how the 2 brands measure up in these criteria.

Warranty: Glow Worm vs Worcester

A boiler is only as good as the warranty on offer; typically, you’ll want a warranty more than 5 years.

In this regard, there’s no problem with the Ultimate 30C — it’s got a long, 5 year warranty. You even have the option to extend it.

When comparing this to the Worcester Bosch combi boiler equivalent, the 30i (Worcester 30i review can be found here), you may be surprised to learn that you get an even better warranty if you purchase through Heatable — a whopping 10 years! And yes, half a decade makes a substantial difference — that’s 5 less years you’ll have to worry about paying out-of-pocket for repairs.

Should You Buy a Glow Worm or a Worcester?

But the biggest difference here is still the price. You’ll be able to pick up a 30C for around £900 (expect to pay around £50-75 more for the 35kW version). That’s well over £2,000 including boiler installation.

Now — we’ve already mentioned Heatable above. Being an online boiler installation company with a ridiculously small overhead, they’re able to supply Worcester boilers at incredibly low prices. In fact, you’ll probably find a Worcester quote (10-year warranty included) that’s comparable in price to the Glow-Worm Ultimate 30C.

Worcester Bosch Greenstar 4000

You can get your quote using Heatable’s clickable form in less than 2 minutes.

Glow Worm Ultimate 30C Boiler Review (30kW)


The first thing you’ll want to focus on is the size. Although Glow Worm’s Ultimate 30C is small, it’s definitely not the most compact boiler on the market.glow worm boiler review

The boiler’s dimensions are 740 x 418 x 300, so you might struggle to fit it into a kitchen cupboard.

Like I said many times before, I like Ideal Boilers. And the Ideal Logic Plus is 700mm x 395mm x 278mm, so it easily fits that into a standard kitchen cupboard.

Central Heating & Hot Water Output

You’ll want to take most boilers’ names with a pinch of salt. Take the Worcester 30i combi boiler for instance; it’s domestic hot water output is 30kW, but the heat output for your radiators is just 24kW.

And this is where the Ultimate 30C fares so much better. It provides a hot water output of 30.6kW (0.6kW more), with a heating output of 30kW. (You can actually trust this boiler’s name).

Compared to the Worcester equivalent, you’ll power an extra 3-4 radiators using the 30C. And this makes the boiler suitable for a slightly larger property than the Worcester 30i.

Energy Efficiency

Both the Worcester 30i and the Ultimate 30C are A-Rated. If you’ve got a boiler that’s 5-years or older, you’re going to save a tonne on your energy bills by replacing it with this Glow Worm boiler. 

If you’re currently using a boiler with an efficiency rating of G (less than 70% efficient), you may see savings of around £840 per year, according to the Energy Saving Trust.

And that’s because A-Rated boilers are usually about 90% efficient. According to the SEDBUK rating 2009 for this Glow Worm boiler, it’s 89.3% efficient, while the 35kW sits at 89.2%.

What kind of fuel does your boiler use?

Fixed price online with next day installation

Worcester boilers from as little as £1,965.


Most boiler components are bought in; they’re not made by the actual boiler manufacturer. And it’s the components the manufacturers choose that make a boiler good or bad.

As an example, there are plenty of reviews of old Vaillant boilers that used to use an unreliable version of a Wilo pump. This device would break, leak, and leave you with a busted boiler and a tonne of water damage.

In the case of the Ultimate 30C (and the 35kW), you needn’t fret over low-quality parts. All Glow Worm Ultimate boilers come with a Grundfos modulating pump, and Grundfos pumps are some of the best in the business.

Frost Protection

If you’ve had a problem with your boiler during winter, there’s a good chance frost protection could have prevented it. Around 20,000 people visited this website in a single day this past winter when the temperature dropped below -6. For most, the fix was probably simple — thaw out the condensate pipe.

Condensed gases are let out of your property via this pipe. And, they’re prone to freezing. When they do, the pipe gets blocked and the boiler locks out.

Luckily, the 30C comes with frost protection, which is designed to keep the boiler ticking over at a few degrees, just enough to stop the condensate pipe (and other parts) from freezing. This means avoiding a boiler lock-out and expensive repair bills.

Glow Worm Boiler Installation Cost

My advice? Get several installers to quote you a range of boiler models.

First, if you want to compare the Ultimate 30C versus Worcester, get your fixed price for a 30i from Heatable.

Next, compare up to 3 quotes from Gas Safe installers here to find a good deal on the Ultimate 30C.

Final Verdict: Should You Buy the Ultimate 30C Boiler?

Glow Worm’s Ultimate 30C isn’t a BAD boiler, but it’s hardly revolutionary either.

In our opinion, your options are (costs for boiler only):

  • Glow worm (around £850-900)
  • Worcester (around £1,100)
  • Ideal Logic Plus (around £900-950)

The cost savings compared to an Ideal just aren’t enough to make me want to buy a Glow Worm. Ideal are good boilers and have 2-years extra warranty (and 5-years extra on their heat exchangers — a good deal, since a replacing faulty heat exchanger is typically a pricey affair).

With Heatable now offering Worcester boiler installation so cheap, that’s where we’d be heading, and picking up a 10-year warranty in the process.

Heatable boiler installations

What’s Next?

Thanks for reading our review of the Ultimate 30C. We constantly update our website with boiler fault finding guides, as well as plumbing, heating and bathroom product reviews; bookmark this page and pop back soon.

Still got questions about replacing your boiler? Leave a comment below and we’ll get back to you as soon as possible.

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