04 error code
04 – Keston Heat² 45/55 error code
What does Keston Keston Heat² 45 and 55 commercial boilers 04 mean?
Keston documents OpenTherm error code 04 for the Heat² 45, 55, 45P and 55P as “Return thermistor short circuit”. The blocking or warning identifies a controller-detected condition on this commercial boiler range.
The code identifies the condition detected by the product; it does not always identify the failed component on its own. Confirm the full code and exact model before ordering parts or attempting a reset.
The Keston Keston Heat² 45 and 55 commercial boilers 04 error code indicates keston documents OpenTherm error code 04 for the Heat² 45, 55, 45P and 55P as “Return thermistor short circuit”. The blocking or warning identifies a controller-detected condition on this commercial boiler range. This guide explains what the code means, the symptoms and likely causes, the checks that are safe to make, and when to stop and arrange an authorised repair.
Symptoms you may notice
The Heat² display reports Fault 04; the affected boiler module may warn, enter a controlled blocking state or lock out, depending on the documented error type.
Common causes
The documented condition relates to return thermistor short circuit. Exact causes can include the named sensor, actuator, combustion, fan, hydraulic, communication, electrical or controller circuit.
Before you start troubleshooting
Use the display, rating label or product menu to confirm the exact model. Similar-looking codes can have different meanings across product generations and regions.
- Record the complete code before switching the equipment off.
- Check only user-accessible controls, filters and external connections described in the manual.
- Do not open gas, refrigerant, combustion or electrical compartments.
Troubleshooting steps
Record Fault 04, its error type and the operating state shown on the display. A qualified heating engineer should test the named circuit using the Heat² installation and service procedures before replacing components.
Can you fix this error code yourself?
The safest next step depends on the exact model and the cause behind the code. External checks may help, but a returning fault needs professional diagnosis.
A successful reset is not proof that the underlying issue is fixed. If 04 reappears, note when it happens and give that information to the service engineer.
Reset instructions
Reset only after the underlying condition has been identified and corrected. Use the display fault-detail screen and reset button only for a resettable lockout; do not repeatedly reset a returning fault.
Applicable products and models
Keston Heat² 45 and 55 commercial boilersHeat² 45; Heat² 55; Heat² 45P; Heat² 55P2020 onwardWhen to contact a professional
Contact Keston commercial support or a suitably qualified Gas Safe registered engineer. Cascade, burner, fan, pump, sensor, parameter and internal-controller diagnosis requires professional access and test equipment.
Frequently asked questions
What does Keston Keston Heat² 45 and 55 commercial boilers 04 mean?
Keston documents OpenTherm error code 04 for the Heat² 45, 55, 45P and 55P as “Return thermistor short circuit”. The blocking or warning identifies a controller-detected condition on this commercial boiler range.
Can I fix Keston Keston Heat² 45 and 55 commercial boilers 04 myself?
Some external checks may be suitable for the user, but the result depends on the exact model and cause. Use the official manual and arrange service if the code returns.
Should I reset the product after code 04?
Reset only after the underlying condition has been identified and corrected. Use the display fault-detail screen and reset button only for a resettable lockout; do not repeatedly reset a returning fault.
When should I arrange a repair?
Contact Keston commercial support or a suitably qualified Gas Safe registered engineer. Cascade, burner, fan, pump, sensor, parameter and internal-controller diagnosis requires professional access and test equipment.