Applicable Systems
Greenstar GB162
Symptoms
The Worcester Bosch Greenstar boiler displays maintenance code H11, indicating a hot water outlet sensor defect. The domestic hot water temperature sensor is faulty, but hot water can still be delivered with less precise temperature control.
Possible Causes
- Hot water outlet temperature sensor (NTC thermistor) failed open or shorted
- Sensor wiring loose or corroded at the connection terminal
- Sensor physically damaged from thermal cycling or water ingress
- Control board sensor input circuit fault (less common)
Troubleshooting Steps
- Step 1: Check sensor wiring connections at the control board and sensor
Connections must be clean, tight, and free of corrosion - Step 2: Measure sensor resistance with a multimeter and compare to temperature-resistance chart
Resistance should match the expected value for the current water temperature; open or zero indicates failure - Step 3: If sensor resistance is out of specification, replace the sensor
Use only genuine Worcester Bosch replacement parts for correct calibration - Step 4: If wiring and sensor are good, the control board sensor input may be faulty
Contact Worcester Bosch support for control board diagnostics
How to Reset
To reset: H11 is a maintenance code, not a locking fault. It does not require a reset. The code will clear automatically once the sensor fault is resolved. Hot water can still be delivered but with less precise temperature control until the sensor is replaced.
Frequently Asked Questions
- Q: Can I still use hot water with H11 displayed?
Yes. H11 is a maintenance code, not a locking fault. The boiler will continue to provide hot water, but the temperature may be less consistent because the outlet sensor is not providing accurate feedback.
- Q: How do I know if the NTC sensor is bad?
Measure the sensor resistance at the current water temperature and compare to the manufacturer's temperature-resistance chart. A typical NTC reads 10k ohm at 25C. Open circuit or near zero indicates a failed sensor.
Source: Worcester Bosch Boiler Error Code Reference, Maintenance Code H11, Worcester Bosch UK Support Documentation
Category: Home Boiler