Glow Worm Ultimate 30c Combi Boiler Review (+ Best Alternatives)

Are you looking for a new boiler in that ‘entry to mid price’ range and come here to see if Glow Worm boilers are any good? Or maybe you have an old Glow Worm boiler that you are looking to replace with a new one. 

Well whatever your plan – you’re in the right place as we are going to cover everything you need to know and find out what the right boiler is for you. 

Fun Fact: One of the most asked questions by potential home buyers to estate agents, after the usual ones, is about the boiler. It’s an actual deciding factor on whether or not buyers like properties. The reason is simple, the surveyor will take care of the big stuff like the condition of the roof and footings but no one wants to move in, find a boiler on the blink and then have to fork out for a replacement. 

Glow Worm Ultimate Boiler Size

For this review we are going to concentrate on the GlowWorm 30c, as that is the most popular model they sell and that’s because it’s best suited for the average 3-4 bed home. 

The Glow Worm Ultimate 30c is a 30kW boiler but they do have a 35kW boiler if you require something slightly bigger. 

Glow Worm Ultimate 30C Vs Worcester 30I

Glow Worm are the entry level boilers, in terms of pricing and that doesn’t mean they are naff, but with boilers you get what you pay for, it’s that simple. Cheaper boilers usually means:

  1. a) lower quality parts 
  2. b) shorter lifespan
  3. c) shorter warranty

If coming up short doesnt sound up your street, the question on most people’s lips is should you instead go with something better, like a Worcester Bosch.

Warranty: Glow Worm vs Worcester

The old saying ‘a boiler is only as good as its warranty’ is still true today. So you need to be placing a big emphasis on the warranty and definitely looking for something over 5 years. As a minimum! 

The good news with the Glow Worm Ultimate 30kW & 35kW you do get a 5 year warranty, so there is nothing to worry about there. Plus there is the option to extend that warranty which is a bonus.    

On paper a 5 year warranty on the Glow Worms sounds great but this falls down when you compare that to the Worcester Bosch 30I boiler which has a 10 year warranty. Literally double Glow Worms warranty. Some Worcester Bosch boilers even have a 12 year warranty, that’s how confident they are behind their products and that confidence feeds through their whole range.

Chances are though you’ve heard of Worcester Bosch and your first thoughts were ‘’hmmm sounds expensive’’ – well 20 years ago you’d have been right, they really were. Still really worth buying with that level of quality and pedigree but nonetheless they were the high end of the price spectrum. Now though, no no no they are sooo much more affordable and still have maintained, infact significantly improved, the quality.

To Buy or Not to Buy: Glow Worm or Worcester?

With all the warranty under the sun it could still be a ‘no go’ because money talks and price is the other deciding factor. 

This is how much you are looking at:

Glow Worm Ultimate 30c Price: £950 upwards [around £1000 for the 35kW model] for the boiler itself PLUS fitting, will bring that in at £2,000. If you’re sitting here reading this with a broken boiler, no hot water and generally feeling miserable you might think ‘’fine, £2k ill pay it’’. WAIT. 

You can get a brand new Worcester Bosch boiler Worcester Bosch boiler for the same price as the Glow Worm Ultimate.

Use Heatable they are the online boiler price comparison site, they are able to offer awesome boilers at amazing prices. Take a look for yourself and you’ll see a new Worcester Bosch 30l boiler which is the competing version of the Glow Worm Ultimate 30c is roughly the same price with fitting. It’s now a no brainer. 


Heatable Worcester-Bosch-Greenstar-i-30kW deal


Heatable are able to give you great prices as they have taken everything online and it saves a fortune, because they have focused on technology rather than having a load of sales reps and you can get a quote for a fixed price in 2 minutes using their clickable form.

Glow Worm 30kW Ultimate Boiler Review

Size & Dimensions

Whilst ‘compact’ it’s definitely not the smallest boiler on the market at 740 x 418 x 300. At that size you could find it tricky to fit it in a kitchen cupboard. Whereas by comparison:

The Baxi 30kW boiler is: 700*390*285

And the Logic Plus is: 700*395*278 

Both of which you could fit and ‘hide’ comfortably in the kitchen cupboard. 

Weight is something manufacturers like to put in the spec sheets and it’s totally relevant in my view. It’s going to be fixed to a wall, you are not going to be carrying it up and down stairs. Ignore. 


Efficiency is everything and so is being green. After all, what’s the point of paying for a better boiler if it doesn’t save you any money on your heating bills. 

The idea should be getting the best boiler you can for the money and then being able to comfortably claw some of that money back in efficiency savings. 

Well good news, both the Worcester 30l and the Glow Worm 30kW Ultimate are ‘A Rated’.

By comparison if you currently have a G rated boiler which has an efficiency rating of less than 70% you could see savings of £155 per year. [According to the Energy Saving Trust]

The SEDBUK rating 2009 for the Glow Worm is 89.3% efficient, and the 35kw is 89.2% efficient.

So over just 10 years that’s nearly paid for the boiler itself in efficiency savings alone! 

So if you are in the position where you are totting up whether to repair your old boiler or buy a new Worcester from Heatable taking advantage of an awesome fixed price & 10 year warranty, based on efficiency alone, it should be clear. New boilers are just far – far more efficient. 

Heating & Hot Water Output

Usually here manufacturers don’t quite do what it says on the tin. So for example the Worcester 30I – it’s hot water output is 30kw and that produces 12.3 litres per minute, but the heating is actually just 24kw. By comparison the BAXI 30Kw flow rate is 12.2 litres per minute too, so slightly above 12 is standard. 

Compare the 24kW heating of the Worcester against the Glow Worm and the Glow Worm will do 30kW of heating. So here the Glow Worm is better than the Worcester 30l, it’s the only point where it is better however but nonetheless that extra output means you could power an extra 3 or 4 radiators. So here the Glow Worm would be more suitable for heating a slightly larger property. 


To cost save, manufacturers no longer make all their own parts, they buy them in and it’s this fact alone that makes all the difference in the overall reliability. Boilers are the sum of all their parts. 

In truth, think of any boiler as a heater that then pumps that heated water around your home. So the pump is a really crucial part. When old boilers break they are usually let down by their pump. Old Wilo pumps for instance were the main culprit for breakdowns.

Fitted in the Glow Worm Ultimate 30kW & 35kW are some respectable parts like the Grundfos modulating pump. Grundfos are well made and well respected amongst engineers. 

If your current Glow Worm boiler is not working with a suspected faulty diverter valve it might not make economic sense to replace the valve. Read more here about faulty diverter valve in general. Read more here about faulty diverter valve in general.


Frost Prevention

Frost prevention is designed, as it sounds, to kick in and prevent the condensate pipe [amongst other parts] from freezing. A freezing outlet pipe will prevent the boiler from firing and can cause breaks. This usually always results in engineer calls out and expensive repair bills for something that can be simply avoided. 

To protect you from any issues the boiler and pump switch on automatically when the temperature falls to a certain level in the heating circuit. 

The hot water circuit is not protected by the boiler and frost protection for the system can only be guaranteed by the boiler. 

So ok frost protection is fairly common now amongst new boilers and that’s the reason why. But honestly it really is better to have it than not have it in the UK with our ‘climate’ as it saves so much hassle and potential repair bills. 

Cost: Glow Worm Boiler Installation 

Boilers are no different from buying anything else, the advice is still the same; get a range of quotes for a number of different boilers that fit your requirements. 

As I’ve stated before, use an online boiler comparison site to check the cost of the Glow Worm Ultimate 30 when comparable to the Worcester Bosch 30l for a fixed price on a new boiler. 


So Whats the Verdict: Should you buy a Glow Worm Ultimate 30?

Emotions aside, for us it comes down to price and warranty; it’s as simple as that:


Glow Worm: circa £950

Worcester: circa £1100

Ideal: circa £950-£1000

Yes there is a cost saving buying a Glow Worm vs buying an Ideal boiler but only maybe a 10% cost saving. But Ideal do have a 7 year warranty [& an extra 5 years more on their heat exchangers] vs Glow Worms pretty basic 5 year warranty. 

But with Heatable offering the best boiler brand [in our opinion] Worcester Bosch for such good value for money that’s where I’ll have to hang my hat. For us the Worcestershire Bosch 30l, which is a competing size boiler to the Glow Worm Ultimate 30c is the far better deal. 

What now?

To get an online quote in 2 minutes for a new boiler, jump over to this price comparison site and pick up a bargain today. Order by 3pm and they offer next day fitting and finance on purchases!

As always I hope you found this guide helpful!