B30 error code
B30 – Flow and return temperature difference too high
What does Keston Keston C45, C40P, C55 and C55P condensing boilers B30 mean?
Keston documents B30 for the C45, C40P, C55 and C55P as “Flow and return temperature difference too high”. This meaning applies to this controller family and should not be transferred to another Keston product without checking its manual.
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 C45, C40P, C55 and C55P condensing boilers B30 error code indicates keston documents B30 for the C45, C40P, C55 and C55P as “Flow and return temperature difference too high”. This meaning applies to this controller family and should not be transferred to another Keston product without checking its manual. 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 display alternates B30 with status 9 and the flow temperature while operation is temporarily blocked.
Common causes
The manufacturer associates B30 with flow and return temperature difference too high, involving the related pressure, circulation, temperature-sensing, fan, ignition, gas, flue-safety 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
A heating engineer should check pump direction and operation, system circulation, air locks, blockages and the flow/return sensors.
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 B30 reappears, note when it happens and give that information to the service engineer.
Reset instructions
The boiler normally retries automatically after the adverse condition clears. Do not force repeated resets if the block keeps returning.
Applicable products and models
Keston C45, C40P, C55 and C55P condensing boilersC45; C40P; C55; C55P2010 manual generationWhen to contact a professional
Contact a suitably qualified Gas Safe registered engineer when a block persists, a lockout returns, or diagnosis requires internal measurements, wiring checks or replacement parts.
Frequently asked questions
What does Keston Keston C45, C40P, C55 and C55P condensing boilers B30 mean?
Keston documents B30 for the C45, C40P, C55 and C55P as “Flow and return temperature difference too high”. This meaning applies to this controller family and should not be transferred to another Keston product without checking its manual.
Can I fix Keston Keston C45, C40P, C55 and C55P condensing boilers B30 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 B30?
The boiler normally retries automatically after the adverse condition clears. Do not force repeated resets if the block keeps returning.
When should I arrange a repair?
Contact a suitably qualified Gas Safe registered engineer when a block persists, a lockout returns, or diagnosis requires internal measurements, wiring checks or replacement parts.