- Boilers
- Gas boiler
F24
Glow-worm F24 on a gas boiler: temperature rises too quickly
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On Glow-worm boilers, F.24 means the water temperature is rising too quickly, usually because water is not circulating well. Check the gauge reads 1 to 1.5 bar, reset once and call your installer (open vented) or a Glow-worm engineer (combi or system).
Safety first
Stop and check this first
- If you smell gas, Glow-worm says to leave the property immediately and call the National Gas Emergency Service on 0800 111 999. Do not operate switches on the way out and make the call from outside.
- If F.24 keeps returning, do not open the boiler to bleed it: Glow-worm sends system and combination boilers to its engineer.
Safe checks you can perform
- Pressure gauge
- Radiators and noises
- One reset
- Venting, circulation and sensor check
Leave these tasks to a qualified professional
- Do not attempt this professional task: Venting and circulation
- Do not attempt this professional task: Sensor and expansion vessel tests
- Do not attempt this professional task: Combustion and flue check
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Venting and circulation
What they doThe engineer vents air from the boiler and system and checks the pump, valves and any blockage.
They must show youflow restored and radiators heating.
In writingwhat was found and done.
Sensor and expansion vessel tests
What they doThe engineer tests the flow and return sensors and checks the internal expansion vessel.
They must show youthe readings.
In writingthe values and the reference of any part replaced.
Combustion and flue check
What they doAfter repair, the engineer checks the flue and measures combustion with an analyser.
They must show youthe analyser printout.
In writingthe readings.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Pressure gauge
- Who:
- you.
- How:
- read the gauge; the normal range Glow-worm gives is 1 to 1.5 bar.
- Result that matters:
- whether pressure is low.
- If it is under 1 bar:
- top up slowly with the filling loop if you feel competent.
- If it is in range:
- air or circulation become more likely.
- Evidence to keep:
- a photo of the gauge.
Evidence: Glow-worm boiler fault codes: what they mean and how to fix them
Radiators and noises
- Who:
- you.
- How:
- with heating on, feel whether radiators heat and listen for gurgling.
- Result that matters:
- signs of air or poor flow.
- If radiators gurgle or stay cold:
- tell the engineer; air or circulation fit F.24.
- If they heat evenly:
- sensors become more likely.
- Evidence to keep:
- a note of which radiators stay cold.
Evidence: Glow-worm boiler fault codes: what they mean and how to fix them
One reset
- Who:
- you.
- How:
- reset the boiler as your user manual describes.
- Result that matters:
- whether F.24 returns.
- If it returns:
- call your installer (open vented) or a Glow-worm engineer (combi or system).
- If it runs:
- keep notes in case it recurs.
- Evidence to keep:
- a note of each reset.
Evidence: Glow-worm boiler fault codes: what they mean and how to fix them
Venting, circulation and sensor check
- Who:
- your installer or a Glow-worm engineer.
- How:
- vents the boiler and system, checks the pump and valves and tests the sensors and expansion vessel.
- Result that matters:
- what slows the water.
- If air or a blockage is found:
- it is cleared.
- If flow is right:
- sensors or vessel are replaced.
- Evidence to keep:
- a job sheet with findings.
On system and combination boilers Glow-worm says not to open the casing; it is a job for its engineer.
Evidence: HSE gas safety for homeowners · Glow-worm boiler fault codes: what they mean and how to fix them
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Glow-worm
- Product type
- Gas boiler
Known code variants
- 24
- anomalía F24 Miele
- anomalie F24 Miele
- code erreur F24 chaudière Vaillant
- code erreur F24 lave-vaisselle Miele
- codice F24 Vaillant
- código F24 Vaillant
- error F24 caldera Vaillant
- error F24 lavavajillas Miele
- Error F24 Saunier Duval
- errore F24 caldaia Vaillant
- errore F24 lavastoviglie Miele
- F 24
- Fehlercode F24 Miele
- Fehlercode F24 Vaillant
- Glow worm boiler F24
- Glow worm F24
- Glow-worm F.24
- Glow-worm F24
- Glow-worm F24 temperature rise
- guasto F24 Miele
- Miele dishwasher F24
- Miele F24
- Miele fault F24
- Miele Geschirrspüler Fehler F24
- panne F24 Vaillant
- Saunier Duval F.24
- ThemaFast Condens F.24
- Vaillant boiler F24 fault
- Vaillant F.24
- Vaillant F24
- Vaillant Fehler F24
What it means
Glow-worm's fault code page gives F.24 as the temperature increasing too quickly. Possible causes it lists are air in the product, system pressure too low, faulty wiring or flow and return sensors, a circulation fault (pump, valve, blockage) and a defective internal expansion vessel. A fast rise means heat is not being carried away from the heat exchanger. Glow-worm sends open vented boilers to the installer and system or combination boilers to its own engineer.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas, Glow-worm says to leave the property immediately and call the National Gas Emergency Service on 0800 111 999. Do not operate switches on the way out and make the call from outside.
Evidence: HSE gas safety for homeowners · Glow-worm boiler fault codes: what they mean and how to fix them
- Mediumsource verified
If F.24 keeps returning, do not open the boiler to bleed it: Glow-worm sends system and combination boilers to its engineer.
Evidence: Glow-worm boiler fault codes: what they mean and how to fix them
Symptoms and causes
Probable causes · in order
- Air or low pressureCommon
Fits after work on the system or when the gauge is low; air pockets slow the water and the temperature shoots up.
Evidence: Glow-worm boiler fault codes: what they mean and how to fix them
- Circulation faultPossible
Fits if the pump, a valve or a blockage restricts flow; radiators heat slowly or unevenly.
Evidence: Glow-worm boiler fault codes: what they mean and how to fix them
- Sensors or expansion vesselPossible
Fits if flow is fine; sensors misreading or a failed vessel can give the same code.
Evidence: Glow-worm boiler fault codes: what they mean and how to fix them
Virtual technician
Does F24 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Health and Safety Executive · official_doc
- 2
Glow-worm boiler fault codes: what they mean and how to fix them
Glow-worm · official_doc
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