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Glow Worm Energy 25c Review

Is your current boiler in need of an upgrade? Think its best days are perhaps behind it? Then keep reading! The Glow Worm Energy 25c boiler may be the best choice if you live in a small house, and if you’re looking for a dependable, budget-friendly option, then this might well be the model you want to consider! 

This Glow Worm boiler model is excellent for particularly small homes, or rooms with restricted space. The Glow Worm energy 25c combi boiler is one of the foremost boilers on the market – not just in terms of technology but also in its design, too. It’s so small that it can even easily fit within an empty kitchen cupboard!

Short Overview On The Glow-worm Energy 25C

Energy combi boiler range Unit 25kW
Boiler dimensions (H x W x D) mm 700 x 390 x 280
Nominal heat output range at 50/30˚C (Condensing mode) kW 5.3 – 19.1
Nominal heat output range at 80/60˚C (Non condensing mode) kW 5 – 18.3
Domestic Hot Water
Lowest water pressure to operate boiler bar 0.2
Domestic hot water flow rate (at DT = Δ30K) l/min 12.1
Heat exchanger material Aluminium
Boiler lift weight (Dry boiler) kg 32
ErP efficiency % 93
ErP decibel rating (sound power) dBa 49
PCDB seasonal efficiency % 89.2
Fluing Options
Maximum horizontal flue length 60/100 m 10
Maximum vertical flue length 60/100 m 10

This boiler is A-rated equipment because of its excellent efficiency rating of 94%. The 25 kW output is perfect for smaller-sized homes that don’t regularly require a large amount of hot water. This boiler is ideal for smaller homes because of its high efficiency. The unit is 700 by 390 by 280 millimeters and small enough to fit in a bathroom or kitchen cupboard, allowing it to be easily hidden from view. 

Having hot water on demand means you won’t need a storage cylinder to keep the water warm for your heating system and your taps. You can also do away with your attic cold water feed tank, because water is fed straight from the mains!

The Pros and Cons

As you might have caught on by now, the Glow-worm Energy 25 C boiler is a good choice when it comes to heating if you have a small home. It is also a great way to save money and reduce your carbon footprint, whilst you’re at it. In addition, the boiler has an average capacity and is simple to repair if needed. However, there are certain disadvantages – especially when you have a larger home.


If you prefer your boilers to be ‘home-grown’ and you are in the UK, then you’ll be pleased to know that Glow worm builds it’s Energy 25C combi boiler in it’s Belper (England) factory. Although Grundfos pumps are installed with the boiler and are a Danish company, but they do provide a high-efficiency modulation included within the Energy combi boiler, which lowers operating costs by adjusting to the actual demand for heating and hot water.

  • ErP A rated combi boiler (94% efficiency).
  • It can be fitted in numerous places – such as kitchen cupboards – because of its small footprint.
  • Flue options at the back provide for greater design flexibility.
  • Quiet Mark signifies that householders can enjoy ultra-quiet operations.
  • You should be able to save money in the long term thanks to its high-efficiency level.
  • The manufacturer’s warranty is 7 years, but you can get up to 10 years.

It’s a good choice for people who live in small flats, due to the boiler’s diminutive size. The flow rate of 12.1 liters per minute is enough for a one or two-bedroom house to be heated. This means that a family of three to four will be able to take showers and baths with no problems.


The Glow-worm Energy 25C can be used in smaller homes, but it may not be enough to keep you warm if you live in a larger household. If  you have a four-bedroom house, for instance, then you may want to explore a boiler model with a larger capacity. Other drawbacks include:

  • Insufficient water flow to allow for more than two showers simultaneously. 
  • Extended warranties of up to ten years are not automatically available (unless installed by a Glow-worm Club Energy Installer, which at Boiler Choice we are!).
  • Programming the controls can be challenging at times.

Our Verdict

The Glow-worm Energy 25C combi boiler is a great choice to replace your old boiler. It’s perfect for small homes and apartments, as it takes up little space. It has an aluminum heat exchanger designed to last longer – and save you money, at the same time. 

In addition, it includes a 10-year manufacturer’s warranty. However, don’t expect much if you have more than two bathrooms and a busy household, given its limited heating capacity and flow rate.

Frequently Asked Questions (FAQs)

• How long is the glow worm Energy 25c warranty?

With a 7-year standard guarantee which is similar to other models with the same price range. You may also want to join the Glow Worm Energy Club to get your warranty upgraded up to 10 years.

• How much is the glow worm Energy 25c?

This low-cost variant typically sells for around £775 at most online retailers. However, the installation cost is not included, which is about £500 for typical installers.

• How much is the glow worm Energy 25c?

A system leak is one of the primary sources of pressure loss. Therefore, you may need assistance locating and repairing a leak in your Glow-worm boiler. After fixing the leak, repressurize your boiler using the instructions below.

  1. Find the filing loop underneath the boiler.
  2. Turn the right tap open.
  3. Open the left-hand tap, and you should hear water entering the system.
  4. Keep an eye on the pressure control; it should be around 1.5 bar.
  5. Close the left tap first, then the right.

• What are the common Glow worm Energy 25c fault codes?

In most cases, when a boiler fault code appears, it means that something is wrong, and you should examine the boiler manual. These are some of the fault codes:

Fault codes
F.00 Fault: Flow temperature sensor NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC sensor defective.
F.01 Fault: Return temperature sensor NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC sensor defective.
F.10 Short circuit: Flow temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing.
F.11 Short circuit: Return temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing.
F.12 and F.91 Short circuit: Cylinder temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing.
F.13 Short circuit: Domestic hot water cylinder temperature sensor NTC sensor defective, short circuit in the cable harness, cable/casing.
F.20 Safety switch-oft. Overheating temperature reached Incorrect earth connection between cable harness and product, flow or return NTC defective (loose connection), black discharge via ignition cable, ignition plug or ignition electrode.
F.22 Safety switch-oft. Low water pressure in the boiler No or insufficient water in the product, water pressure sensor defective, cable lo the pump or to the water pressure sensor loose/not connected/defective.
F.23 Safety switch-oft. Temperature difference too great (NTC1/NTC2) Pump blocked, insufficient pump output, air in the product, flow and return NTC sensor connected the wrong way round.

Interested in a Glow Worm Energy 25c boiler or another type of boiler installation?

If so, you can schedule an appointment with us by visiting the product page for our Glow Worm Energy 25c boiler.  You may also speak to a member of our staff at Boiler Choice on 0800 112 3433 or email us at [email protected].