70 error code
70 – Keston Heat² error code
What does Keston Keston Heat² 45, 55, 45P and 55P boilers 70 mean?
Keston identifies OpenTherm fault 70 on Heat² 45, 55, 45P and 55P boilers as “Heat-exchanger water-flow fault below minimum flow rate”. The manual classifies it as a blocking fault.
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, 55, 45P and 55P boilers 70 error code indicates keston identifies OpenTherm fault 70 on Heat² 45, 55, 45P and 55P boilers as “Heat-exchanger water-flow fault below minimum flow rate”. The manual classifies it as a blocking fault. 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 lists fault 70. Depending on the classification, the boiler may continue with a warning, enter a controlled blocking state or lock out until the condition is corrected.
Common causes
The control has detected heat-exchanger water-flow fault below minimum flow rate. The exact cause can involve a thermistor or its wiring, temperature supervision, water flow or pressure, flame proving, fan or pump feedback, communications, supply voltage, configuration or an internal control condition.
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
With the system cold, check only the visible pressure and user-operable external valves. Internal pump, flow-sensor and hydraulic checks require a qualified engineer.
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 70 reappears, note when it happens and give that information to the service engineer.
Reset instructions
A blocking fault may clear when its cause is corrected. Do not repeatedly power-cycle or reset the boiler to suppress a returning fault.
Applicable products and models
Keston Heat² 45, 55, 45P and 55P boilersHeat² 45; Heat² 55; Heat² 45P; Heat² 55P2020 product generationWhen to contact a professional
Contact Keston while the appliance is under warranty, or a suitably qualified Gas Safe registered engineer (or the locally competent person), when the fault persists, recurs or requires internal testing or repair.
Frequently asked questions
What does Keston Keston Heat² 45, 55, 45P and 55P boilers 70 mean?
Keston identifies OpenTherm fault 70 on Heat² 45, 55, 45P and 55P boilers as “Heat-exchanger water-flow fault below minimum flow rate”. The manual classifies it as a blocking fault.
Can I fix Keston Keston Heat² 45, 55, 45P and 55P boilers 70 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 70?
A blocking fault may clear when its cause is corrected. Do not repeatedly power-cycle or reset the boiler to suppress a returning fault.
When should I arrange a repair?
Contact Keston while the appliance is under warranty, or a suitably qualified Gas Safe registered engineer (or the locally competent person), when the fault persists, recurs or requires internal testing or repair.