Start with the pattern you can observe
Tell the plumber whether the water is never warm enough, starts normally and then cools, or changes when another tap is used. Include whether the behaviour affects every hot outlet or just a particular shower. Those differences help define the assessment.
Don't put your hand in unexpectedly hot water to test a system, and don't ask children to compare temperatures. A qualified provider can measure the supply appropriately. This guide is for recording the symptom, not testing safety settings.
Use the repairs page to arrange an enquiry. If you have electric storage, the electric system guide explains why heating times belong in the brief. The system planning tool is useful if household demand has changed.
Explain what happens before it cools
For stored hot water, mention how many showers or baths happened before the change. Tell the provider if the system heats on a controlled supply, if you know. A household using more water than before is a different starting point from an unchanged household noticing a new fault.
For a continuous-flow appliance, describe simultaneous outlet use and any visible controller message. Avoid assigning a cause from a general internet list. Different models have different controls and fault behaviour.
A single outlet is useful information
If the rest of the home still has normal hot water, make that clear in the message. The attending provider may need to check the affected fixture and associated plumbing as well as the heater. Replacing the heater without identifying the fault can leave the original problem unresolved.
If all outlets changed at once, include any recent work, outage or change to normal controls. Keep a short timeline of what happened. Don't remove covers or alter mixer, tempering or safety-valve settings in an attempt to make the symptoms match a diagnosis.
Don’t turn up a safety setting as an experiment
Stored water temperature and delivered outlet temperature serve different purposes. Their safe operation depends on the installation and relevant requirements. A general article can't specify the right adjustment for an uninspected system.
Use the manufacturer's own instructions and have the appropriately licensed provider assess the equipment. The Australian Government's smart hot-water guidance flags the importance of safe heating temperatures. CBS guidance explains checking a plumber's licence.
Keep the first visit clearly scoped
Ask what the assessment fee covers, which parts of the installation the provider expects to inspect and how any repair will be quoted. If a capacity issue is identified, ask the installer to explain it using your actual usage pattern and heating schedule.
You can send an enquiry with the symptom and what you've observed. If a replacement option follows the assessment, use the cost guide to compare the full installed scope. You don't need to choose a new unit before the existing problem is understood.