Inlet water too cold — Winter inlet drops to 5–10°C. Longer heating time is normal.
Temperature set too low — Raise to 50–55°C.
Scale buildup — After 1–2 years without descaling, efficiency drops. Book a descaling service.
Multiple taps running — Stagger usage to avoid running out.
Flow rate too high (tankless) — Reduce flow slightly for higher output temperature.