Worcester A1 fault: pump running dry or no flow detected

Things worth knowing about an A1 flow fault

• Air in the pump head is normal after radiator changes and needs venting
• A full magnetic filter starves flow long before it blocks completely
• Check isolation valves under the boiler are fully open
• Seized pumps often restart once and then fail again within days
• Repeated A1s should never be reset-and-ignored

What is actually going on with an A1 flow fault

The most common triggers are trapped air in the pump head after any drain-down, a pump that has seized after a summer of standing still, a blocked magnetic filter that has never been emptied, or closed service valves left shut after work elsewhere on the system. Sensor and PCB faults sit at the end of that list, not the start.

Where we deal with this

• Nailsea (BS48) · 14 mi
• Larkhall (BA1) · 9 mi
• Wells (BA5) · 10 mi

Questions we get asked

Can I clear the air myself?

Bleeding radiators is safe; venting a pump head involves opening the wet side of the appliance and is engineer work.

Does A1 mean the pump is dead?

Not always. Around half the A1s we attend are flow restriction rather than pump failure.