Ariston DHW Modulation / Flow Regulation Fault

Boiler shows 703, DHW temperature fluctuates, burner cycles rapidly during hot water use

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 DHW plate heat exchanger, Faulty modulating gas valve, Incorrect flow sensor readings, PCB modulation control fault

Safety: Gas valve and combustion adjustments must be done by a Gas Safe engineer.

Check flow rate: Excessively low or high flow can cause instability. Adjust tap opening to a moderate flow and see if temperature stabilises.
Descale plate heat exchanger: A scaled DHW plate heat exchanger restricts flow and causes rapid temperature changes. Professional descaling or replacement is often required.
Engineer checks: An engineer will verify DHW sensor readings, test the modulating gas valve, and adjust combustion if necessary.

Professional Required 5/5

DHW Plate Heat Exchanger

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