ATAG Primary Heat Exchanger Temperature Differential Fault

Furnace displays F7, often with noisy operation or kettling sounds

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Scaled or partially blocked primary heat exchanger, Insufficient system flow, Failing circulation pump

Safety first: Turn off power and allow the boiler to cool completely.

Check system pressure and bleed radiators to ensure good circulation.
Verify that all isolation valves on the boiler flow and return are fully open.
Listen to the circulation pump; if noisy or very hot, it may be failing or air-locked. Vent the pump carefully.
If kettling (boiling) noises persist, the primary heat exchanger may be scaled and require chemical cleaning or replacement by a professional.

Hard 4/5

ATAG primary heat exchanger

Check Price on Amazon

We may earn a commission from links on this page.