Water is leaking or the pump needs replacing or freeing due to the pump running dry
The A1 error code on Worcester boilers indicates water is leaking or the pump needs replacing or freeing due to the pump running dry.
Worcester A1 means: water is leaking or the pump needs replacing or freeing due to the pump running dry. The usual causes are pump seized due to prolonged inactivity or sludge, air lock in the pump or pump motor electrical fault. You can safely reset the boiler once — if A1 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does A1 Mean
The A1 code is shown by the boiler’s control board when it detects water is leaking or the pump needs replacing or freeing due to the pump running dry. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows A1 and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 10 technical sources.
| Cause |
|---|
| Pump seized due to prolonged inactivity or sludge |
| air lock in the pump |
| pump motor electrical fault |
| pump impeller damaged or blocked with debris |
| wiring fault between pump and PCB |
| pump running dry (no water in system) |
Safety Warning
A1 involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
1. Check if the pump is running — listen for humming. A running pump should be warm but not hot. 2. If the pump is humming but not circulating, it may be air-locked — bleed via the pump bleed screw. 3. If seized, try freeing the impeller with a flat screwdriver through the pump centre spindle (with power off). 4. Check the pump speed setting — it should be appropriate for the system size. 5. Measure the voltage at the pump terminals to confirm the PCB is supplying power. 6. Check for debris in the pump by removing and inspecting the impeller
How to Fix It
Free a seized pump by turning the impeller manually
bleed air from the pump
if the pump motor has failed, replace the pump
flush the system to remove sludge and fit a magnetic filter
replace damaged wiring
Refer to the Worcester service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Worcester models that can display fault code A1:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Worcester models | — | Possible |
Frequently Asked Questions
Free a seized pump by turning the impeller manually. According to the technical documentation, this is the first check on the list for A1.
A1 is not classified as a high-severity fault, so the boiler can be reset once. If A1 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.