Intervention of the primary exchanger temperature limiter or of the flue gas temperature limiter
The E9 error code on Bosch-Junkers boilers indicates intervention of the primary exchanger temperature limiter or of the flue gas temperature limiter.
Bosch-Junkers E9 means: intervention of the primary exchanger temperature limiter or of the flue gas temperature limiter. On this component the documented failure modes are flue or air intake blocked or restricted. You can safely reset the boiler once — if E9 returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does E9 Mean
The E9 code is shown by the boiler’s control board when it detects intervention of the primary exchanger temperature limiter or of the flue gas temperature limiter. 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 E9 and the boiler stops until the fault is cleared |
Common Causes
The manufacturer does not publish a cause list for this specific code. The causes below are the failure modes documented for the same component on other boilers, confirmed by the service literature of 7 different manufacturers.
| Cause |
|---|
| Flue or air intake blocked or restricted |
Safety Warning
E9 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.
How to Fix It
Check the correct system pressure, refill the system if necessary and vent any air present, check the delivery NTC sensor, the circulation pump, and the fuse on the electronic board
Check system pressure, temperature limiter, pump operation
vent the appliance
NTC sensor and power cable interrupted or shorted. Check and replace if necessary. Check the operating pressure of the heating system. Check and if necessary replace the temperature sensor. Check and replace them if necessary
Inspect the flue and air intake along their whole length, including the outside terminal, and clear any obstruction or debris.
Refer to the Bosch-Junkers service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Bosch-Junkers models that can display fault code E9:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Bosch-Junkers models | — | Possible |
Frequently Asked Questions
Check the correct system pressure, refill the system if necessary and vent any air present, check the delivery NTC sensor, the circulation pump, and the fuse on the electronic board. According to the technical documentation, this is the first check on the list for E9.
E9 is not classified as a high-severity fault, so the boiler can be reset once. If E9 comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.