- Boilers
- Gas boiler
A1
Worcester A1 on a gas boiler: pump has run dry
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
On the Greenstar CDi Classic, A1 means the boiler pump has run dry, usually because the heating circuit lacks water. Read the gauge: below 1 bar, top up to 1.5 bar with the filling link, reset for 3 seconds and call a Gas Safe engineer if A1 returns.
Safety first
Stop and check this first
- Do not keep topping up and resetting: if pressure keeps falling, water is escaping and Worcester asks you to contact your installer.
- If you smell gas: do not smoke or strike matches, do not operate electrical switches or unplug anything, do not use the phone or ring doorbells. Turn off the gas at the meter, open windows and doors, warn your neighbours and leave. Well away from the building, call the National Gas Emergency Service on 0800 111 999.
Safe checks you can perform
- Pressure gauge reading
- Re-pressurising with the filling link
- One reset
- Leak, pump and venting check
Leave these tasks to a qualified professional
- Do not attempt this professional task: Pump check
- Do not attempt this professional task: Air purge and test run
- Do not attempt this professional task: Leak search and re-pressurising
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.
Pump check
What they doWith the power isolated, the engineer checks whether the pump is seized or has bearing noise, then frees or replaces it.
They must show youthe pump running after venting.
In writingwhether it was freed or replaced, the part reference and why.
Air purge and test run
What they doThe engineer runs service function 2.C, an eight minute venting sequence, vents the radiators and runs the boiler on heating and hot water.
They must show youa full heating cycle with no code.
In writingthat venting was done and the final pressure.
Leak search and re-pressurising
What they doThe engineer checks the boiler and system for water leaks, repairs them and fills, bleeds and re-pressurises as the installation instructions say.
They must show youwhere the water was escaping and the gauge holding after the repair.
In writingwhat leaked and what was repaired.
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 reading
- Who:
- you.
- How:
- with the boiler cold, read the system pressure gauge on the front. Worcester gives 1.5 bar as the optimum and says that below 1 bar the boiler may stop.
- Result that matters:
- the reading in bar.
- If it is below 1 bar:
- re-pressurise as in the next check; lack of water fits A1.
- If it is 1 bar or more:
- lack of water is less likely; air or the pump move up the list.
- Evidence to keep:
- a photo of the gauge with the date and time.
Evidence: Worcester Greenstar CDi Classic combi user instructions 6 720 812 179
Re-pressurising with the filling link
- Who:
- you, following the user instructions.
- How:
- remove the bottom panel, pull down the filling link lever to let mains water in and push it back up when the gauge reads 1.5 bar.
- Result that matters:
- whether the pressure holds over the next days.
- If it falls again:
- the system is leaking; Worcester asks you to contact your installer when the gauge shows a permanent significant drop.
- If it holds:
- carry on with one reset.
- Evidence to keep:
- the gauge reading noted each day for a week.
Evidence: Worcester Greenstar CDi Classic combi user instructions 6 720 812 179
One reset
- Who:
- you.
- How:
- press the reset button for three seconds; the button and fault light stop flashing if the fault clears.
- Result that matters:
- whether the boiler runs without A1.
- If A1 returns:
- stop; Worcester says not to try to rectify listed faults yourself and to call a Gas Safe registered engineer.
- If it runs normally:
- note the date; a repeat points to air or the pump.
- Evidence to keep:
- a photo of the display before the reset and a note of the time.
Evidence: Worcester Greenstar CDi Classic combi user instructions 6 720 812 179
Leak, pump and venting check
- Who:
- a Worcester or other Gas Safe registered engineer.
- How:
- looks for leaks, checks whether the pump is seized or has bearing noise and runs the air purge mode.
- Result that matters:
- which step of the booklet clears A1.
- If venting clears it:
- air was the cause.
- If the pump is seized or noisy:
- it is freed or replaced.
- Evidence to keep:
- a job sheet listing what was found.
Draining the boiler, opening the casing and pump work are engineer jobs; Worcester tells users not to rectify listed faults themselves.
Evidence: Worcester Greenstar CDi Classic combi user instructions 6 720 812 179 · Worcester Greenstar CDi Classic engineer's service booklet 6 720 830 033
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
- Worcester Bosch
- Product type
- Gas boiler
Known code variants
- A01
- A 1
- A1 281
- A1 Worcester
- aire acondicionado Daikin A1
- Cerapur A1
- climatisation Daikin A1
- climatizzatore Daikin A1
- code erreur A1 Daikin
- codice A1 Daikin
- código A1 Daikin
- Daikin A1
- Daikin AC A1
- Daikin error A1
- Daikin Fehler A1
- Daikin Fehlercode A1
- E:A1
- EA1
- error A1 Daikin
- Error A1 Junkers
- errore A1 Daikin
- Fujitsu A1
- Fujitsu E A1
- Greenstar A1
- Junkers A1
- Klimaanlage Daikin A1
- panne A1 Daikin
- Worcester A1
- Worcester boiler A1 fault
- Worcester Bosch A1
What it means
Worcester's service booklet for the Greenstar CDi Classic describes A1 as the controlled characteristic pump having run dry. The engineer first checks whether system pressure is below 1.2 bar, then whether the pump is seized or sticking, whether its bearings are audibly damaged and whether air must be purged with the venting sequence (service function 2.C). The code reports what the pump control detects; it does not tell a leak, trapped air and a worn pump apart.
Warnings and stop conditions
- Highsource verified
Do not keep topping up and resetting: if pressure keeps falling, water is escaping and Worcester asks you to contact your installer.
Evidence: Worcester Greenstar CDi Classic combi user instructions 6 720 812 179
- Criticalsource verified
If you smell gas: do not smoke or strike matches, do not operate electrical switches or unplug anything, do not use the phone or ring doorbells. Turn off the gas at the meter, open windows and doors, warn your neighbours and leave. Well away from the building, call the National Gas Emergency Service on 0800 111 999.
Evidence: Worcester Greenstar CDi Classic combi user instructions 6 720 812 179
Symptoms and causes
Probable causes · in order
- Low system pressure or a leakCommon
Fits when the gauge reads below 1 bar. If pressure drops again after topping up, water is escaping from the system or the boiler.
Evidence: Worcester Greenstar CDi Classic combi user instructions 6 720 812 179 · Worcester Greenstar CDi Classic engineer's service booklet 6 720 830 033
- Air in the heating circuitPossible
Fits after draining, refilling or radiator work: pressure can look right while the pump turns without water around it. The engineer clears it with the air purge mode.
Evidence: Worcester Greenstar CDi Classic engineer's service booklet 6 720 830 033
- Pump seized or with worn bearingsPossible
Fits when pressure is correct and A1 keeps returning. The booklet has the engineer free a sticking pump and replace it if the bearings are noisy.
Evidence: Worcester Greenstar CDi Classic engineer's service booklet 6 720 830 033
Virtual technician
Does A1 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
Worcester Greenstar CDi Classic combi user instructions 6 720 812 179
Worcester Bosch · 2014 · manual
- 2
Worcester Greenstar CDi Classic engineer's service booklet 6 720 830 033
Worcester Bosch · 2014 · manual
Was this entry useful?