Hot water temperature fluctuates or runs hot then cold during shower use

Safety first: Beware of sudden hot water temperature spikes that can cause scalding.

User checks:

• Ensure the hot tap or shower is fully open to maintain a steady flow.
• Avoid mixing hot and cold at the shower if the boiler is sensitive to low flow; adjust at the boiler controls instead.

Engineer checks:

• Check DHW NTC sensor readings and replace if faulty.
• Inspect and descale or replace the plate heat exchanger.
• Verify minimum flow rate through the boiler and adjust any flow restrictors if necessary.
• Check external thermostatic mixing valves for correct operation.

Stable DHW temperature depends on clean heat exchangers and accurate sensing.