How to Fix ATAG 133 Fault Code (No Flame During Run) UK
ATAG 133 means no flame during run. UK diagnosis, parts to order, reset sequence.
What 133 means
ATAG 133 indicates no flame during run. The boiler will lock out and refuse to fire until the fault is cleared.
Do not simply reset — 133 is stored in the ATAG error log and will re-trigger within minutes if the underlying part has failed.
Diagnostic sequence
Enter service mode on the ATAG boiler and read the flow/return/DHW temperatures, fan PWM, ionisation current and pump speed.
Cross-reference against the ATAG technical manual — 133 typically points to two or three candidate parts.
- Check wiring harness continuity to the suspect sensor before condemning it.
- Isolate at the fused spur, discharge and re-inspect connectors.
- Measure resistance / voltage at the PCB plug per ATAG test procedure.
Parts to have on the van
Carry a set of NTC sensors, an ignition electrode kit and a fan for ATAG — these three parts clear >70% of 133 call-outs.
Recommission
After the fix, run the ATAG boiler through a full flow test, gas rate, and combustion analysis. Log to the Benchmark book to preserve manufacturer warranty.
Frequently asked questions
- Can I reset 133 without changing parts?
- Only if the fault has cleared (e.g. low pressure repressurised). Persistent 133 means a hardware failure.
- Which is the most common cause of ATAG 133?
- On ATAG boilers, 133 most often points to the sensor or actuator matching its meaning (no flame during run); check wiring and connector integrity first.
- Is a Gas Safe engineer required?
- Yes — any works past the boiler case seal require a Gas Safe registered engineer under UK law.
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