Gas Safe registered
Glow-worm specialists
Energy, Ultimate, Betacom and the older Flexicom. Twenty years on Glow-worm boilers, rates agreed beforehand, and parts guaranteed for a year.
Answered 24 hours a day by a technical customer service member.
A Betacom shows the fault as a flashing temperature rather than an F code, so 60 on the display may not be a temperature at all.
No heating or hot water right now? Call 0203 868 6134. We will tell you the earliest realistic slot rather than the one you want to hear.
Two details to start. Add the fault code and your postcode and we can usually tell you the likely part before we attend.
Three steps, no sales pitch, and you will know where you stand before an engineer is booked.
A Glow-worm is worth repairing more often than its reputation suggests. It is the brand people are quickest to write off, usually because it was the cheapest boiler on a developer's schedule rather than because anything is wrong with it. The parts are current, the platform is shared with a major manufacturer, and we will tell you plainly when a repair is the better spend.
Glow-worm failures cluster around the water side rather than the gas side, which is unusual and useful to know. Six parts cover most of it.
Glow-worm has been part of the Vaillant Group since 2001, so most ranges report faults as an F followed by two digits. But the meanings shift between ranges more than they do on most makes, and two whole families of Glow-worm do not show codes at all.
What the boiler is saying: system pressure has fallen under roughly 0.6 bar, which is too little to fire safely. It is the most common Glow-worm code by a wide margin.
What you can safely do: open the filling loop until the gauge reads between 1 and 1.5 bar cold, close it fully, then reset once. This is the one Glow-worm code most householders can clear themselves.
Rarely the cause: a boiler fault. The boiler is reporting the water in your pipework.
On some ranges low pressure appears as F9 instead, or as a red indicator on models without a numeric display. Same fault, same fix.
Topping up more than once a month? Tell us before you refill it again.
The boiler ran its ignition sequence and never saw a flame, so it locked out.
The seasonal answer first. In cold weather this is very often the condensate pipe, frozen where it runs outside, and it is the single biggest cause of Glow-worm breakdowns in winter. Pour warm water along the pipe, never boiling, which splits it. On some ranges the same cause shows as F1, F4 or F29 instead, which is why generic code lists disagree about what F28 means.
The rest of the year: the ignition electrode and its lead, then the gas valve, then a partly blocked flue.
Check first: does the hob light? Is there credit on a prepayment meter? An F28 with no gas anywhere is not a boiler fault.
Rarely the cause: the circuit board, which locked the boiler out rather than continuing to release gas into an appliance that was not burning it.
Is it freezing outside? That question changes the answer completely.
Different from F28, and the difference decides the repair. F28 never lit. F29 lit, ran, then dropped out.
The likely cause: a gas supply that sags once the boiler is drawing properly, a condensate route that is blocked rather than fully frozen, or flue gases recirculating into the air intake from a damaged or badly sited terminal.
Rarely the cause: worth spending money on parts before the flue and the gas pressure at the appliance have both been checked. A recirculating flue makes perfectly healthy components read as faulty.
Does it happen on heating, hot water, or both? That narrows it.
The boiler started the pump and did not see the pressure change it expected, so it locked out before lighting.
Where Glow-worm differs: this is the same code, on the same platform, as the one Vaillant use, because the two brands share a parent company and a great deal of engineering. What differs is the likelihood. On a Glow-worm of seven to ten years old the pump is a realistic candidate rather than the long shot it usually is elsewhere.
How to narrow it before anybody attends: stand next to the boiler when the heating calls. A pump that hums has power and has probably seized. A pump that is silent has either failed or is not being told to run, and those are different repairs.
The other two candidates: the pressure sensor silted with magnetite, or an expansion vessel that has lost its air charge. Both are cheaper than a pump and both should be ruled out first.
Why it comes back: change the sensor and leave the vessel flat and the code returns within weeks. Clearing the sludge out stops the sensor silting again.
Humming, or silent? That one word narrows this a long way.
F16 points at the fan or its wiring. F5 and the codes around it are the overheat family, which on Glow-worm is very often airlocks rather than anything mechanical.
The fan: as on most makes, it announces itself. A Glow-worm that has been noisier than it used to be for several weeks is telling you this is coming.
The overheat codes: these appear disproportionately after somebody has worked on the system, because refilling introduces air and air is what stops the water carrying heat away. If the boiler started doing this within days of a radiator being changed or a leak being fixed, say so, because it points straight at the cause.
What helps most: bleeding the system properly, then checking whether the automatic air vent on the boiler is doing its job.
Has anybody worked on the heating recently? That detail matters here.
This is the Glow-worm quirk that sends more people down the wrong path than anything else on this page.
The Betacom range has no F code display. It reports faults by flashing one of the temperature numbers on the panel, so 30, 40, 50, 60, 70, 80 or 90 will flash to tell you what has gone wrong. The number is a fault reference, not a water temperature.
Why it matters: somebody sees 60 flashing, assumes the boiler is running at 60 degrees, and cannot work out why there is no heat. Or they search for a Glow-worm fault code 60 and find nothing, because it is not an F code.
What to do: note which number is flashing and whether anything else on the panel is lit, then tell us. Low pressure is the most common of them and is often something you can clear yourself once you know that is what it is.
Also worth knowing: a flashing yellow indicator on a Betacom is often about the temperature control knobs rather than a fault, and adjusting them clears it.
Which number is flashing? Tell us that and we can usually name it.
Older Compact models and several other Glow-worm ranges use indicator lights rather than a display. Red, amber and green, sometimes steady and sometimes flashing, and the combination is the fault.
What to note: which colours are lit, which are flashing, and how many flashes there are in a burst before it pauses and repeats. That count is the code. On some ranges a red light flashing a set number of times is doing exactly the same job as an F number.
The most common one: a red indicator usually means low pressure, which is the same easy fix as F22 above.
What to do: photograph the panel while the fault is showing. A photograph is worth more than a description and it saves an engineer working it out from scratch on the doorstep.
Describe the lights over the phone and we can usually place it.
| Code | What the boiler is saying | What it usually turns out to be |
|---|---|---|
| F1 | Ignition or flame sequence problem | In winter, the condensate. Otherwise the electrode |
| F4 | Flame sensing or condensate related | Read alongside F28, meaning varies by range |
| F5 | Overheat | Air in the system, especially after recent work |
| F9 | Low pressure, on some ranges | Read exactly as F22 above |
| F11 / F13 | Sensor or cylinder sensor fault | The sensor or its plug, and F13 names the cylinder |
| F20 | Safety limiter tripped | Circulation, not the burner |
| F27 | Flame seen with the gas valve shut | Moisture on the electronics |
| F61 / F62 | Gas valve drive or shut off | The valve or the board, and a test separates them |
| S codes | Status, not a fault | What the boiler is doing at that second |
Glow-worm code meanings genuinely vary between ranges, which is why two reputable websites will tell you different things about the same number. An F1 on one range is not always an F1 on another. The manual for your specific model is the only list that is definitely right about your boiler, and if you cannot find it the range name and serial number will get an engineer to the correct one in under a minute.
Glow-worm sits in a particular place in the market, and that position produces a set of problems the premium brands do not have.
Glow-worm has been part of the Vaillant Group since 2001. That is not a marketing detail, it changes the answer to the question people most often ask us about this brand, which is whether it is worth repairing.
What it means in practice: the engineering is shared, a great many components are the same or near identical, and the parts supply is far deeper than a budget badge would suggest. An engineer who knows Vaillant knows most of what is inside your Glow-worm.
What it does not mean: that a Glow-worm is a Vaillant with a different sticker. The specification differs by range, and the cheaper Glow-worm ranges are built to a price in ways that show up over a decade rather than in the first year.
The practical upshot: do not let anybody write your boiler off on the badge alone. The parts almost certainly exist. Whether the repair is worth it is a question about the specific part, not the brand.
Glow-worm is the brand developers and landlords fit most often, because it meets the specification at the lowest cost. If you moved into a flat and inherited the boiler, there is a good chance nobody who chose it ever had to live with it.
What that means for you: the boiler is often the smallest output that satisfied the calculation, so it can be genuinely undersized for how the property is actually used. A 24 kilowatt combi that was adequate for a one bathroom flat becomes marginal once somebody adds a second shower.
How to tell the difference: a faulty boiler fails. An undersized one works perfectly and simply cannot keep up, so the hot water fades when two things run at once and the heating takes a long time to recover after a cold night.
Why it matters: the second of those is not a repair. Replacing parts will not fix it, and anybody selling you parts for it is not solving your problem. That is a replacement conversation, and an honest one.
Does it fail, or just never quite keep up? Different answers. Call 0203 868 6134.
Glow-worm made a range designed to sit inside a standard kitchen cupboard, and plenty of London flats have one. From the room you see a cupboard door and nothing else.
Why it matters when you book anybody: access is a real factor. A boiler in a cupboard with a worktop over it and units either side takes longer to work on, and if a part sits at the back it may mean removing a unit. An engineer who arrives expecting a wall hung boiler has not allowed for that.
What to check yourself: whether the cupboard has any ventilation, and whether anybody has stacked cleaning products or towels around the boiler. Both matter, and one of them is a genuine safety point rather than a tidiness one.
Tell us when you call: say it is in a unit and describe what is around it. It changes what an engineer brings and how long we allow.
The pump is the part we replace most often on this brand, and between roughly seven and ten years old it is a genuinely common failure rather than an unlucky one.
What you will notice: a low hum or buzz from the boiler when the heating calls, no radiators getting warm anywhere, and often no fault code at all in the early stages because the boiler cannot tell the difference between a pump that is not running and a pump that is running badly.
What to check before booking: stand next to it when the heating switches on. Humming means it has power and has probably seized. Silence means either the pump has failed completely or it is not being asked to run, which is a different and usually cheaper problem.
Worth knowing: on most Glow-worm models the pump head changes without draining the system down, so this is a shorter job than people expect when they hear the word pump.
Humming or silent when the heating calls? Call 0203 868 6134.
Worth repairing more often than you have been told
This is the brand people are quickest to write off, usually because it was the cheapest boiler on a developer's schedule rather than because anything is wrong with it. The parts are current and the platform is shared with a major manufacturer.
The label is behind the front panel. With Glow-worm the range name is the important part, because it decides how the boiler reports a fault as well as what parts it takes.
Glow-worm name the range, then the output, then a letter for the type. An Energy 30c is an Energy range combi rated 30 kilowatts.
If your letter is anything other than c, there is stored hot water somewhere in the house and the cylinder is as likely to be the fault as the boiler is.
Energy and Ultimate are the current ranges and the ones most often on London walls now. Digital display, F codes.
Flexicom, Ultracom and Xtramax are the previous generation and also use F codes, though the meanings shift between them.
Betacom is the one to identify early, because it reports through flashing temperature numbers rather than codes. If your display shows temperatures and nothing else, this is probably yours.
Compact, Micron and Hideaway are older still. Some use indicator lights only, and the Hideaway is the range designed to live inside a kitchen unit.
This matters more on Glow-worm than on most makes. The ranges have been revised repeatedly, code meanings differ between them, and a part that fits one Energy does not always fit another.
The serial number and GC number on the label identify exactly which revision is on your wall, and they are also what gets an engineer to the correct fault code list rather than a generic one.
Photograph the label before you call anybody. It takes a moment and on this brand it is the difference between a confident answer on the phone and an educated guess. That advice applies to every boiler brand we repair, without exception.
London is a hard water city almost everywhere, and that is the single biggest difference between repairing a Glow-worm here and repairing one in Manchester or Glasgow.
Roughly 277 milligrams of calcium carbonate per litre is the London average, with districts running from about 250 to over 350. The chalk comes from the Chilterns and the North Downs, which the Thames and the Lea both pass through on the way here. For a combi the consequence is specific rather than general: scale builds in the plate heat exchanger, and it builds faster than the service schedule assumes.
It is the same story in Islington and Highbury as it is in Epsom and Ewell. The water is hard, the plate heat exchanger scales, and the only question is whether anybody checks it before condemning the boiler.
Hardness is not uniform, and it does not follow borough boundaries. It varies by supply zone and can change over a short distance, so your supplier publishes a figure for your own postcode and it is worth reading before anybody guesses.
Scale drops out of solution faster the hotter the water gets. A combi set to deliver taps at 65 degrees furs up its plate heat exchanger noticeably faster than one set to 50, which is still hot enough to scald. Turning that dial down costs nothing and is the most effective thing a householder in a hard water area can do. This applies to the tap setting, not to a cylinder, which must reach 60 degrees for safety.
Plenty of London houses still store their hot water, and a combi is not a substitute for it.
Most firms here are combi-only, which does not suit a city with this many larger properties. A Glow-worm system or heat only boiler runs a stored cylinder with its own thermostat, immersion element and, if unvented, its own safety devices. When the hot water goes the boiler takes the blame, and more often than not the boiler is fine and the fault is in the cupboard.
The cylinder sensor is a small part in a pocket on the tank, and when it fails the boiler simply stops heating your stored water while the heating carries on faultlessly. Inexpensive, quick, and invisible to anybody looking only at the boiler.
The motorised valve routes heat to the radiators or the cylinder. A failed motor or microswitch produces heating without hot water, or the reverse, or both running when you asked for one. The head normally changes without draining the system.
The immersion element scales until it trips or stops. It is worth testing rather than assuming, because an element costs far less than a tank. Across the larger properties in Fulham and Parsons Green a scale reducer usually goes in at the same time.
An unvented cylinder is a pressure vessel. It carries an expansion vessel, a pressure reducing valve, an expansion relief valve and a temperature and pressure relief valve, all discharging through a tundish. Water running at the tundish means one of them has failed. Do not leave it and never cap it off.
Unvented work is notifiable and needs a G3 qualification on top of Gas Safe registration. Our engineers hold both, so the boiler and the cylinder are dealt with on one visit rather than two appointments and two charges. That is why unvented cylinder repair sits alongside the boiler work instead of being farmed out.
Swapping stored hot water for a combi to free an airing cupboard is the change people most often ask us to reverse. A combi cannot run two showers at once, whatever the output on the box, because it heats water as it passes rather than storing it. In a house with three bathrooms the honest answer is usually to keep the cylinder and spend the money replacing it if it is old, rather than removing it.
This is the brand people are quickest to give up on, and often too early. Age alone does not decide it. Which part has failed decides it.
| What has failed | Under 8 years | 8 to 14 years | 15 years and older |
|---|---|---|---|
| Pressure sensor, flow and return sensors | Repair | Repair | Repair if parts exist |
| Ignition and sensing electrodes | Repair | Repair | Repair if parts exist |
| Expansion vessel, pump | Repair | Repair | Repair |
| Fan | Repair | Repair | Depends on the rest of the boiler |
| Diverter valve, plate heat exchanger | Repair | Repair | Repair if the part is still made |
| Gas valve | Repair | Depends on the rest of the boiler | Replace |
| Control board | Check the guarantee first | Borderline, we will be straight with you | Replace |
| Main heat exchanger | Guarantee claim if registered | Usually replace | Replace |
Every part is current and at this age almost every failure is a single component. An electrode, sensor, fan or pump on a six year old Energy is a repair, without qualification.
This is where the brand gets treated unfairly. A Glow-worm and a premium boiler of the same age with the same failed sensor are the same repair at the same cost, but only one of them gets suggested for replacement. Ask which part has failed and what that part costs on its own before you accept a quote for a new boiler.
Check the guarantee first, including with us. Glow-worm registered guarantees run for a set term from installation and plenty of people have cover they have forgotten about.
Still a clear repair: electrodes, pressure sensor, fan, expansion vessel, diverter valve. Ordinary wear items that say nothing about the rest of the boiler.
Expect the pump somewhere in this band. It is the single most likely part to need replacing on a Glow-worm at this age, and it is still comfortably a repair rather than a reason to replace the appliance.
The conversation changes with a main heat exchanger, or a second significant failure inside a year. At that point the arithmetic favours replacing the boiler, and the question is what goes in the next two winters as much as what has gone today.
Past this point availability takes over from cost. The older Glow-worm ranges are the ones most likely to stop being repairable, and a Compact or a Micron can be mechanically sound and still finished because one part is no longer made.
The Hideaway adds a second problem, because a boiler built into a kitchen unit is a larger job to replace than a wall hung one. That should be reflected in a quote from the start rather than appearing halfway through the work.
We check availability before you pay for anybody to attend and tell you what has failed. See our guide to repair and replacement costs for what the number is made of.
Local boiler repair specialists
Clear advice. Careful repairs. Family-friendly service.
Call 0203 868 6134London, north and south of the river. These are the districts we work in most.
These are where we work most, not a boundary. An engineer attends anywhere in north London and south London. Tell us where you are and we will say plainly when we can get to you.
If you smell gas: do not touch any switches. Open the windows, leave the property, then call the National Gas Emergency Service on 0800 111 999. That line is free and open 24 hours. Call them before you call us.
If a carbon monoxide alarm is sounding: get everyone out immediately, then call 999 if anyone feels unwell. Do not go back in until the property has been ventilated and checked.
If the boiler locks out repeatedly: try one reset. If it locks out again straight away, stop. Repeated resets hide a fault that is still there, and on a gas appliance that is not a risk worth taking.
Under the Gas Safety (Installation and Use) Regulations 1998, only a Gas Safe registered engineer may work on gas appliances. Never open the boiler casing yourself.
Usually, yes. F22 means system water pressure has fallen below roughly 0.6 bar, too little for the boiler to fire safely. Open the filling loop until the gauge reads between 1 and 1.5 bar cold, close it fully and reset once. What you cannot fix is why it dropped: once a year is normal, every few weeks means a leak, every few days usually means the expansion vessel has lost its charge. On some ranges the same fault appears as F9 or as a red indicator instead.
On a Betacom, that is the fault code. The range has no F code display and reports faults by flashing one of the temperature numbers on the panel, so 30, 40, 50, 60, 70, 80 or 90 flashing is a fault reference rather than a water temperature. It catches people out badly, because searching for a Glow-worm code 60 finds nothing. Note which number is flashing and what else is lit, and tell us. Low pressure is the most common of them.
Not quite, but they are closely related. Glow-worm has been part of the Vaillant Group since 2001, the engineering is shared and a great many components are the same or near identical, which is why the parts supply is far better than a budget badge suggests. What differs is specification: the cheaper Glow-worm ranges are built to a price in ways that show over a decade rather than in the first year. The practical point is that parts almost certainly exist for yours.
The boiler started the pump and did not see the pressure change it expected, so it locked out before lighting. Three candidates: the pump, the water pressure sensor silted with magnetite, or an expansion vessel that has lost its air charge. On a Glow-worm between seven and ten years old the pump is a realistic candidate rather than a long shot. Stand next to it when the heating calls, because a hum means power and a probable seizure, while silence means something different.
Because the meanings genuinely vary between ranges. An F1 on one Glow-worm range is not always an F1 on another, and the older ranges use lights or flashing temperatures rather than numbers at all. Generic code lists flatten those differences and end up wrong for somebody. The manual for your specific model is the only list guaranteed to be right about your boiler, and the range name plus serial number will get an engineer to the correct one quickly.
The label is behind the front panel. Glow-worm name the range, then the output, then a letter for the type, so an Energy 30c is an Energy range combi at 30 kilowatts. The letter matters: c is a combi, s is a system boiler, h or r is heat only, and anything other than c means there is a hot water cylinder somewhere in the house. Photograph the label, because on this brand the serial number is what gets an engineer to the right parts and the right code list. We work on every make of boiler.
More often than people assume. It is the brand most quickly written off, usually because it was the cheapest boiler on a developer's schedule rather than because anything is wrong with it. Under eight years old, repair it. Between eight and fourteen, expect the pump at some point and treat that as a repair rather than a verdict. On a Compact, Micron or Hideaway past fifteen, availability starts to decide it. See our boiler replacement page.
It depends on the part, and that is not evasion. A price given before anybody has asked what your boiler is doing is invented. Three things decide the figure: the part itself, whether we are carrying it or ordering it, and the time on site. On a Glow-worm the code and the range name together usually tell us which part before anybody attends. The rate is agreed beforehand and parts we fit are guaranteed for a year, so nothing is carried out on the assumption that you will approve it afterwards. There is no charge for telling you a repair is not the right call. See our guide to repair and replacement costs for what the number is made of.
Glow-worm sits alongside Vaillant and Saunier Duval in the same group, which is why an engineer who knows one of them tends to know all three.
No gas supply? Plenty of London flats run without one, and we also cover electric boiler repair.
A Glow-worm gets written off earlier than it deserves, on the badge rather than the fault. Give us the range name and the code, or a description of the lights, and we will say plainly whether a repair is the better spend.
Gas Safe registered. Unvented cylinder qualified. Parts guaranteed for a year. Covering London, north and south of the river, 24 hours a day.
