cc
E09Boiler & heater codes

Bosch Combi Boiler Error E09 — Flow / Return NTC Sensor Fault

The boiler cannot read a plausible temperature from the flow or return sensor.

Severity: mediumBosch Condens / Class condensing boilersJunkers-Bosch (Bosch Thermotechnik)

Technical meaning

The NTC thermistor on the flow or return line reports a value outside the valid range (open or short circuit).

Symptoms

  • No domestic hot water
  • Heating stays cold
  • Boiler locks out after a few seconds
  • Display alternates between E09 and the temperature

Most likely causes

  1. 1Temperature sensor (NTC) or its wiring is broken or corroded
  2. 2System pressure below 1 bar, so the sensor measures air instead of water
  3. 3Air lock or a closed radiator valve blocking circulation

How to fix it

  1. 1Press and hold the Reset button for about 3 seconds and wait for the restart.
  2. 2Read the pressure gauge: top the system up to between 1.5 and 2.0 bar with the filling loop.
  3. 3Open all radiator valves and bleed the radiators to remove trapped air.
  4. 4Switch the boiler off at the mains, wait 30 seconds, then power it back on.
  5. 5Check the NTC connector on the PCB for corrosion; reseat it carefully.
  6. 6If E09 returns immediately after every reset, the sensor must be measured and replaced by a technician.
Reset & basınç kontrolü
1. Reset tuşuna 3 saniye basılı tutun
2. Su basıncını 1.5 - 2.0 bar arasına ayarlayın
3. Kalorifer vanalarının açık olduğunu doğrulayın
4. Cihazı kapatıp 30 saniye bekleyin ve yeniden açın
5. Hata tekrarlarsa servis çağırın

Frequently asked questions

Can I keep using the boiler with E09?
No. The boiler blocks heating and hot water to protect the heat exchanger from overheating.
How much does an NTC sensor cost?
The part is usually cheap; the labour and the pressure check dominate the bill.

Copies: 38,220 · Views: 96,540 · Updated: Sep 12, 2026

Related entries

OBD-II P0300 — Random / Multiple Cylinder Misfire Detected

P0300

The ECU detected misfires on several cylinders without a single identifiable source.

errors

iPhone Error 4013 — Restore / Update Failed (USB Connection)

4013

Finder or iTunes lost the USB connection while flashing the device firmware.

errors

Bosch Boiler Error EA — No Flame Detected

EA

The boiler tried to ignite but the flame sensor never confirmed a flame.

errors