Domestic hot water temperature fluctuates between hot and cold during use.

Safety first: Be cautious of sudden temperature spikes that can cause scalding.

• Check inlet filters: Clean any cold water inlet filters or strainers to ensure stable flow through the boiler.
• Avoid low flow rates: Very low tap flows can cause instability. Increase flow slightly and see if temperature stabilizes.
• Descale plate heat exchanger: Limescale can cause rapid overheating and cooling. A technician should chemically descale or replace the DHW plate exchanger.
• Sensor and flow checks: Have a technician verify flow sensor operation and temperature sensor accuracy.