Makes we repair
Which 24i do you have?
Your 24i is one of three Worcester combis sold under that name, one after another. The three are the 24i RSF, the 24i junior and the Greenstar 24i junior, each with a 28i sister that works the same way.
The name on the front, the lights and whether the boiler has a condensate pipe tell the three apart.
Worcester 24i RSF (and the 28i RSF)
Made
About 1998 to 2003
How to tell it
Non-condensing. A strip of controls across the bottom holds one small mains light above the heating knob, and a round pressure gauge. An overheat cut-off button sits on top of the case
Still made?
No longer made
Worcester 24i junior (and the 28i junior)
Made
About 2003 to 2005
How to tell it
Non-condensing. A wide oval control panel runs across the lower front. The panel holds a flame light, a fault light that is also the reset button, the heating knob and a round pressure gauge
Still made?
No longer made
Worcester Greenstar 24i junior (and the 28i junior)
Made
About 2005 to 2015
How to tell it
Condensing, with a condensate pipe to a drain. The case is white. Behind a flap across its lower front are a blue power and fault light, a green burner light, a reset button and the pressure gauge
Still made?
No longer made
Where the name is depends on the range:
- A 24i RSF has its name on the lower trim.
- A 24i junior has its name on the oval control panel.
- A Greenstar 24i junior has its name on the case. Its details, the G.C. number among them, are under the controls flap.
A condensate pipe, and a plume from the flue outside when it runs, mean a Greenstar.
A name that looks alike: the Greenstar 24i System is a different boiler. It is a system boiler, which heats a hot water cylinder. It was made from about 2005, and its ErP version is still listed as current in the government's database. Everything below is about the three 24i combis.
Not a 24i? See every Worcester Bosch boiler and how each shows a fault, or every make we repair, by type.
Sources: the government's boiler database for the years, and Worcester's user instructions and installation manuals for each range.
Worcester 24i lights and what they mean
A Worcester 24i shows a fault with lights, not a numbered code, and each range has its own:
- a 24i RSF has one mains light
- a 24i junior has a flame light and a fault light
- a Greenstar 24i junior has a blue power and fault light, a green burner light and a reset button that flashes
The same light can point to more than one fault. The same fault also shows differently on each range, so each panel below sets out all three. The first six panels are the faults Worcester's user guides explain to owners. The last three hold every light, range by range.
LockoutAn ignition lockout: the burner didn't light
What it means: The 24i tried to light its burner, didn't, and has locked out. Each range shows it in its own way:
- On a 24i RSF no light changes, and the burner gave up after 10 seconds.
- On a 24i junior the fault light flashes slowly, about once a second.
- On a Greenstar 24i junior the blue light flashes slowly, mostly off, and the reset button flashes.
Possible causes, as the manuals list them:
- the gas supply and its pressure
- the gas valve
- the combustion and the flue
- a blocked or frozen condensate pipe (on the Greenstar, in its 2013 manual)
- the ignition electrodes and their leads
- the main board
The 24i junior's manual adds low water pressure, the pump, the sensors, the overheat thermostat and a blocked burner or heat exchanger.
What you can do: see that the gas supply is on, then reset once, as your range's guide shows:
- On a 24i RSF, turn the heating knob to the summer position and back. The boiler tries again after about four minutes.
- On a 24i junior, hold the reset button in for five seconds.
- On a Greenstar 24i junior, press the reset button.
The steps are in the reset and top-up section below.
If it locks out again, ring us. If you smell gas, don't reset anything. Ring the National Gas Emergency Service on 0800 111 999. We'll ask which lights are on, and how they flash.
OverheatAn overheat lockout: a safety thermostat has cut out
What it means: The water in the 24i got too hot, and the overheat cut-off stopped the burner. Each range shows the overheat differently:
- On a 24i RSF the fan or the pump runs, but there is no spark and no flame.
- On a 24i junior the fault light flashes slowly, as it does for an ignition lockout.
- On a Greenstar 24i junior the blue light flashes slowly, mostly on, with the reset button flashing, for a flue or heat exchanger overheat.
Possible causes, as the Greenstar's manual lists them:
- a blocked heat exchanger
- the water pressure
- air in the system
- the pump
- leaks or blockages
- the safety thermostats
- the wiring
- the main board
What you can do: read the pressure gauge, as the panel on low pressure shows. Then reset once:
- On a 24i RSF, press the overheat cut-off button on top of the case.
- On a 24i junior, let the boiler cool, then hold the reset button in for five seconds.
- On a Greenstar 24i junior, press the reset button.
If it cuts out again, ring us. The 24i RSF's manual says a cut-off that trips at once, or often, points to a serious problem.
PressureLow water pressure: the heating is short of water
What it means: The water pressure in the 24i's sealed heating system has fallen. A 24i has no light of its own for low pressure. Low pressure is listed instead among the causes of other faults:
- On a 24i junior, low pressure is among the causes its manual gives for a slow flash.
- On a Greenstar 24i junior, low pressure is among the causes of a heat exchanger overheat, with the blue light flashing slowly, mostly on.
What Worcester's guides say:
- The 24i junior's guide gives 1 to 1.5 bar as normal, and 2.5 bar as the most.
- The Greenstar's 2013 guide says to top up below 1 bar.
- The 24i RSF's and 24i junior's guides leave topping up to the way the installer showed you.
- The 2005 Greenstar guide says the cause of a loss should be looked into.
What you can do: top up as your range's guide shows. The steps are in the reset and top-up section below.
If the pressure keeps dropping, or rises, ring us. A leak, or radiators that need bleeding again and again, is an engineer's job, the 24i junior's guide says. We'll ask what the gauge reads.
FlueAn air flow or flue fault: the boiler can't sense its air
What it means: The 24i hasn't sensed air flowing through it as it should, so it has locked out to stay safe. The signs differ by range:
- On a 24i RSF no light changes, and the boiler relights by itself once the air flow is back.
- On a 24i junior the fault light flashes quickly, and the boiler tries again after about 5 minutes.
- On a Greenstar 24i junior a flue overheat shows as the blue light flashing slowly, mostly on. Its 2009 manual lists a blocked flue the same way.
Possible causes, as the manuals list them:
- the fan
- the air pressure switch or condensation in its tubes
- a blocked flue
What you can do: look at the flue's outlet outside, from the ground. Worcester's guides say not to use the boiler if the outlet is blocked or damaged, so switch it off and ring us. The air pressure switch is a safety device inside the case, and the engineer's to look at.
SensorA sensor fault: a temperature sensor or its wiring
What it means: A temperature sensor in the 24i, or its wiring, has a fault. The light that shows depends on the range:
- A 24i RSF's mains light flashes.
- A 24i junior's fault light flashes quickly, the same light as an air flow fault.
- A Greenstar 24i junior's blue light flashes quickly with the reset button unlit. Its manual calls this a volatile lockout, and its 2013 manual adds that the fan doesn't run.
Possible causes, as the manuals list them:
- the sensor (a thermistor) or its wiring
- on a Greenstar, the fan, its lead or the code plug
- the main board
What you can do: on a 24i junior, switch the power off and on once at the switched socket, as its guide says. There is nothing else to do at home, as a sensor is an engineer's repair.
Frozen pipeA condensate pipe that has frozen (Greenstar 24i junior)
What it means: The Greenstar 24i junior is the condensing 24i. Its condensate pipe can freeze where it runs outside, or through an unheated space such as a garage. The boiler then shuts down with its reset light flashing. The non-condensing 24i RSF and 24i junior have no condensate pipe.
What you can do, as the 2013 guide shows: thaw a pipe at ground level that is easy to reach, never one at height. The guide's steps are:
- Find the frozen point, often the open end, a bend or a dip.
- Warm it with a hot water bottle, a microwavable heat pack, a cloth soaked in hot water, or hot water poured from a watering can. Never use boiling water.
- Then hold the reset button for five seconds.
- Give the boiler two to three minutes to restart.
If it doesn't restart, or the pipe freezes again, ring us. We'll ask where the pipe runs.
MoreEvery light and lockout on the 24i RSF
A 24i RSF has one mains light, so most of its lockouts show no change of light at all. Each entry is from its user instructions and its installation manual.
Mains light offNo mains electricity is reaching the boiler
What Worcester's papers give
The supply, then the fuses inside, then the main board. All three are an engineer's checks
Mains light onThe power is on
What Worcester's papers give
Normal running
Mains light flashingA sensor fault
What Worcester's papers give
The hot water and heating sensors (thermistors) or their wiring, then the main board
No change of light, with the fan or pump running but no spark and no flameThe overheat cut-off has operated, and the boiler has locked out
What Worcester's papers give
Press the overheat cut-off button on top of the case. If it won't stay in, the checks are the thermostat and its capillary
No change of light, and the burner didn't light in 10 secondsAn ignition lockout
What Worcester's papers give
End the call for heat by turning the heating knob to the summer position and back. The boiler tries again after about four minutes. Then look at the gas supply, and call an engineer if it keeps happening. The installation manual also clears it by switching the power off for a few seconds
No change of light, with the gas valve shut and no air flow sensedAn air flow lockout
What Worcester's papers give
The boiler relights once the air flow is back. The checks are the flue outlet outside, then the fan and the air pressure switch
MoreEvery light on the 24i junior
A 24i junior has a flame light and a fault light, and the fault light flashes slowly or quickly. Each entry is from its user instructions and its installation manual.
Flame light on, or offThe burner is on, or off
What Worcester's papers give
Normal running
Fault light flashing slowly, about once a secondAn ignition lockout, or an overheat
What Worcester's papers give
Hold the reset button in for five seconds (after an overheat, once the boiler has cooled). The manual's list starts with the gas supply or its pressure, a weak spark, the gas valve, and low water pressure or a dry boiler. The list goes on to the pump, the main sensor's position, the flame sensor and the overheat thermostat. Last come a blocked burner or heat exchanger, the wiring and the board
Fault light flashing quicklyA fault in the boiler. Its user guide shows an air flow fault this way
What Worcester's papers give
Switch the power off and on at the switched socket. After an air flow fault, the boiler tries again after about 5 minutes. The manual's list starts with a heating or hot water sensor out of place or faulty. Next come the air pressure switch or condensation in its tubes, a failed or stiff fan, a blocked flue, the wiring and the board
Fault light flashing quickly, in the manual's tableThe gas valve's mode switch left at its lowest or highest setting
What Worcester's papers give
An engineer's setting, not a fault at home
No lights, and nothing workingNo power
What Worcester's papers give
The power supply, a fuse, the transformer or the board
Heating dead, hot water workingNo call for heat is reaching the boiler
What Worcester's papers give
The room thermostat and the programmer, then the board
Hot water dead, heating workingA fault on the hot water side
What Worcester's papers give
The flow sensor, the hot water sensor or the board
Burner on with nothing calling for heatThe built-in frost thermostat at work, or the board
What Worcester's papers give
Normal in cold weather
Water too hot, or not hot enoughA sensor off its pipe, low gas pressure, a setting, a sticking gas valve or flow sensor, or the board
What Worcester's papers give
An engineer's checks
MoreEvery light on the Greenstar 24i junior
A Greenstar 24i junior pairs its blue light with the reset button, and the two together point to the fault. Each entry is from its 2013 installation manual. The 2005 and 2009 manuals differ in detail, so the engineer reads the manual for your boiler's date.
Blue light off, with the reset button unlitNo power at the control board
What the manual lists
The mains supply, the boiler's switch, the fuses, the transformer (in the 2009 manual), then the board
Blue light on, with the reset button unlitNot working for heating, for hot water or for either, or running with no call for heat
What the manual lists
The room thermostat or timer, the heating knob, the diverter valve, the hot water flow sensor, the fan or the board
Blue light flashing slowly, mostly off, with the reset button flashingAn ignition lockout
What the manual lists
The gas and its pressure, the gas valve, the combustion, the flue, the ignition electrodes and leads, and the board. The 2013 manual adds a blocked or frozen condensate pipe
Blue light flashing slowly, mostly on, with the reset button flashingA flue or heat exchanger overheat. The 2009 manual adds a blocked flue
What the manual lists
A blocked heat exchanger, the water pressure, air in the system, the pump, leaks or blockages, the safety thermostats, the wiring, the board
Blue light flashing quickly, with the reset button unlitWhat the manual calls a volatile lockout. In the 2013 manual, the fan doesn't run
What the manual lists
The temperature sensors and their leads, the fan and its lead, the code plug
Blue light flashing quickly, with the reset button flashingAn internal fault
What the manual lists
An engineer's reset of the board, then a new board
Blue light pulsing twice, or five times, with the reset button unlitNot a fault: service mode set to its lowest or highest output
What the manual lists
Press the service button to go back to normal
The causes in each panel are in the order the manuals give them, not ranked by how often they happen.
Sources: Worcester's user instructions and installation manuals for the 24i RSF, the 24i junior and the Greenstar 24i junior, from 2000 to 2013, from Worcester Bosch's own literature pages, read on 11 October 2026.
How do you reset a 24i, and top up its pressure?
A 24i is reset its own way on each range, as its user guide shows. Whichever you have, reset it once:
- 24i RSF: an ignition lockout clears when the call for heat ends. Turn the heating knob to the summer position and back, or let the room thermostat or programmer end its call. The boiler tries again after about four minutes, and straight away for hot water. After an overheat, press the overheat cut-off button on top of the case.
- 24i junior: when the fault light flashes slowly, hold the reset button in for five seconds. The fault light is the reset button itself. After an overheat, let the boiler cool, then hold the button. When the light flashes quickly, switch the power off and on at the switched socket. The junior's guide also clears an ignition lockout the RSF's way, by ending the call for heat.
- Greenstar 24i junior: push the flap at its top centre to open it, and press the reset button. The 2013 guide says to hold it for about five seconds. After a power cut, the 2009 guide says the boiler may need resetting this way too.
If the light comes back, or the boiler won't relight, ring us. A lockout that keeps returning is an engineer's job. A 24i has no pilot light to relight, as every range lights itself with a spark. The safe checks for any boiler that won't light are on the page on a boiler that won't fire up.
Topping up: the pressure gauge sits with the controls. Worcester's guides give 1 to 1.5 bar as the usual pressure and 2.5 bar as the most.
On a 24i RSF or a 24i junior, top up the way the installer showed you. A 24i RSF's gauge has a red needle for the pressure the boiler needs, and a grey one for the pressure now.
On a Greenstar 24i junior, top up below 1 bar, as its 2013 guide shows. Take off the bottom panel to find the filling link, then follow the steps for your link:
- A keyless link: pull the blue lever down, and let go at 1 to 1.5 bar.
- A keyed link: fit the key and turn it to the closed padlock. Open the white knob, close it at 1 to 1.5 bar, then take the key out.
- An external filling loop: fit the hose and open both valves a quarter turn. Close them at 1 to 1.5 bar, then take the hose off and refit the caps.
Ring us if the pressure keeps dropping or rises, if nobody showed you how to top up, or if you can't find the filling loop. We'll ask what the gauge reads.
In a frost: leave a Greenstar 24i junior's power on, as its guide says, so its frost protection can run. The 24i RSF and 24i junior have built-in frost protection for short spells.
Sources: Worcester's user instructions for the 24i RSF and the 24i junior, its user guides for the Greenstar 24i junior of 2009 and 2013, and the three ranges' installation manuals.
Is a 24i worth repairing?
A 24i is often worth repairing. Age alone doesn't decide it. Three things do:
- whether the part can be had
- the rate for the repair, against a new boiler
- how often the boiler has failed
The choice is yours.
Age and parts. The three ranges' ages in 2026 are:
- a 24i RSF, about 23 to 28 years
- a 24i junior, about 21 to 23 years
- a Greenstar 24i junior, about 11 to 21 years
Worcester's own site has said it stocks spare parts for at least 10 years after a boiler stops being made. Its spares catalogue still lists the Greenstar 24i junior, and parts for the 24i junior, without showing what is in stock. The engineer tells you whether the part your 24i needs can be had before any repair is agreed. We are an independent firm, with no connection with Worcester Bosch.
Worcester's own view on age: a boiler serviced every year should last 10 to 15 years, and some run for 20 or more. Worcester counts harder-to-find parts among its signs that a boiler is due for a change.
Today's rules for a new boiler apply when one is replaced. Those rules don't make a working 24i unlawful, though the non-condensing 24i RSF and 24i junior couldn't be fitted new today.
A new boiler is the other road. We fit new boilers too, with Worcester Bosch among the makes we fit most. Each new boiler is sized with a heat loss calculation, and quoted from photos of the old boiler or after a free survey visit. A condensing boiler in a non-condensing 24i's place needs a pipe to carry its condensate to a drain. See what a new boiler includes, and how the day goes. Not sure which way to go? Ring us, and we'll ask what the boiler is doing.
Sources: the government's boiler database, and Worcester Bosch's spares catalogue, its word on spare parts and its guide to how long a boiler lasts.
15% off a new boiler, fitted
The 15% comes off the price of a new boiler installation. We quote from photos of your old boiler, or after a free survey visit. Now is the time to replace an old or discontinued boiler.
Terms: 15% off everything in the price we quote for a new boiler installation. That means the boiler, its flue and controls, and the fitting. The offer is for installations booked by 31 December 2026. One offer per home, and not with any other offer.
Do you cover my part of London?
Yes: we travel all over Greater London, day and night, to repair Worcester 24i boilers in every borough, north and south of the Thames. We fit new boilers in their place too. Pick your side of the river to see the areas.
North of the river
Every borough north of the Thames: Barnet and Enfield at the top, Hillingdon in the west, Havering in the east, and central London in between.
South of the river
Every borough south of the Thames: Richmond and Kingston in the west, Bexley in the east, and down through Croydon to Sutton and Bromley.
24i: your questions
Does a Worcester 24i have fault codes?
No, a Worcester 24i has no numbered fault codes. Every 24i shows a fault with lights. A 24i RSF has one mains light, and a 24i junior a flame light and a fault light. A Greenstar 24i junior has a blue power and fault light, with a reset button that flashes. What each pattern means is in the lights section above. If a light keeps coming back, ring us.
Is my 24i a Greenstar?
Your 24i is a Greenstar if it has Greenstar on its case, and a condensate pipe running from the boiler to a drain. There is often a plume from the flue outside when it runs. The 24i RSF and 24i junior are non-condensing, with neither. A Greenstar also has a white case with a flap across its lower front, and a blue light behind it.
Is the Greenstar 24i System the same boiler?
No, the Greenstar 24i System isn't the same boiler. It is a system boiler, which heats a hot water cylinder, while every 24i on this page is a combi. The System was made from about 2005, and its ErP version, from 2015, is still listed as current in the government's boiler database. We repair it too. See every Worcester Bosch boiler and how each shows a fault.
Is the Worcester 24i discontinued?
Yes, the Worcester 24i is no longer made, and none is in Worcester's range today. The government's boiler database gives these final years:
- about 2001 or 2003 for the 24i RSF
- about 2005 for the 24i junior
- about 2015 for the Greenstar 24i junior
Worcester still publishes the 24i's user guides and manuals on its website. We repair every 24i, wherever the part can be had.
How do I reset a Worcester 24i?
Resetting a Worcester 24i depends on its range:
- On a 24i RSF, turn the heating knob to the summer position and back to clear an ignition lockout. After an overheat, press the overheat cut-off button on top.
- On a 24i junior, hold the reset button in for five seconds when the fault light flashes slowly. When it flashes quickly, switch the power off and on.
- On a Greenstar 24i junior, press the reset button, for about five seconds by the 2013 guide.
Reset once, and if the light comes back, ring us.
Why has my Greenstar 24i junior stopped in cold weather?
A frozen condensate pipe can stop a Greenstar 24i junior in a frost. The pipe freezes where it runs outside or through a cold space, and the boiler shuts down with its reset light flashing. Thaw a pipe at ground level that is easy to reach. Use a hot water bottle, a heat pack or a cloth soaked in hot water, never boiling water. Then hold reset for five seconds, and give the boiler two to three minutes. If it won't restart, ring us.
Can you still get Worcester 24i parts?
Parts for a Worcester 24i depend on its range and on the part itself. Worcester's own site has said it keeps spare parts for at least 10 years after a boiler goes out of production. The Greenstar 24i junior, and parts for the 24i junior, are still in its spares catalogue, which doesn't show what is in stock. The engineer tells you which part has failed and whether it can be had. The rate is agreed in writing before any repair starts.
How much does a 24i repair cost?
The cost of a 24i repair depends on the part it needs, how long the job takes and when it's done. Our rates are higher in the evening, overnight and at weekends. Once the engineer has found the fault, the rate is agreed in writing before any work starts. See how our rates work.
Do I need to know which 24i I have?
No, you don't need to know which 24i you have. Ring and say what the boiler is doing, and we'll ask the rest. The name on its front, and which lights are on, help if you can see them, but finding the fault is the engineer's job.
Don't know what has failed? You don't have to.Ring and say what you can see or hear. Finding the fault is our job.
Calls answered 24 hours a day
A real person answers and gives you the rate on the call. No work starts until you say yes, and repairs are guaranteed for 12 months: parts, labour and any return visit.
