Boiler runs but hot water temperature fluctuates or goes cold during shower

Safety first: Risk of scalding if temperature suddenly rises. Test water carefully before use.

• Check other taps: See if the issue occurs at multiple outlets or only one (which may indicate a local mixer problem).
• Maintain steady flow: Avoid opening and closing taps rapidly; keep a consistent flow to help the boiler modulate correctly.
• Clean shower mixer filters: Some thermostatic mixers have filters that can clog and affect temperature stability.
• Technician service: A Nibe technician can descale or replace the Nibe plate heat exchanger and verify DHW sensor and flow sensor operation.