Bosch A1: Pump / Low-Water Fault
What the Bosch A1 error code means, what causes it, and why it's a job for a licensed BC gas technician — not a DIY reset.
Severity
High — needs prompt professional attention
What the Bosch A1 error code means
The boiler detected a circulation or low-water problem and shut down to protect itself.
On Bosch Greenstar and Singular series, A1 is a water-flow / circulation fault. It is a protective response — the boiler is telling you something needs attention, and the safe, lasting fix is a proper diagnosis rather than repeated resets.
Symptoms you may notice
- No or weak heat
- Overheat or flow faults under load
- Pump running but rooms stay cold
Common causes of Bosch A1
Why this is not a DIY fix
Low-flow and circulation faults stem from a failing pump, trapped air, a stuck valve, or a blocked strainer. A technician measures actual flow and finds the restriction rather than masking it — protecting the heat exchanger from overheating.
In British Columbia, gas work must be performed by a TSBC-licensed gas fitter. GasBoilers.ca — a CanroHeat division — sends Red Seal–certified, gas-licensed technicians who diagnose the true cause, repair it correctly, and verify safe operation before they leave.
How our technicians diagnose & repair it
- 1Test circulator-pump operation and speed
- 2Purge trapped air and check for air-bound zones
- 3Inspect zone/mixing valves and strainers for blockage
- 4Confirm correct flow rate and stable temperatures
Related Bosch codes
Bosch A1 — FAQ
What does the Bosch A1 error code mean?
The boiler detected a circulation or low-water problem and shut down to protect itself. On Bosch Greenstar and Singular series, this is categorised as a water-flow / circulation fault.
What causes Bosch A1?
The most common causes are: Pump fault / seized; Air-bound system; Low pressure; Blockage. A licensed technician confirms which one applies before any part is replaced.
Can I fix Bosch A1 myself?
No. Low-flow and circulation faults stem from a failing pump, trapped air, a stuck valve, or a blocked strainer. A technician measures actual flow and finds the restriction rather than masking it — protecting the heat exchanger from overheating. Repeatedly resetting the boiler without fixing the root cause can be unsafe and can cause further damage. Call GasBoilers.ca at 604-359-1081 for a licensed diagnosis.
Is the Bosch A1 error code dangerous?
This is a protective fault — the boiler has shut down a function to protect itself. It is best diagnosed promptly by a licensed technician so the underlying cause does not lead to a more expensive failure.
How much does it cost to fix Bosch A1 in Greater Vancouver?
Cost depends on the root cause and any parts needed. We start with a flat-rate diagnostic, then quote the repair before any work begins — no surprises. Call 604-359-1081 for current pricing and same-day availability.
Look up another brand's error codes
Bosch showing A1? We'll fix it right.
Licensed, Red Seal–certified gas technicians across Greater Vancouver. Upfront pricing, same-day service available.