Start by identifying the type of system
The reason for no hot water depends heavily on how the property heats it. A combination boiler produces hot water on demand. A cylinder stores hot water and may be heated by a boiler, immersion heater or both. Some homes have older vented systems with tanks in the loft. Before testing anything, work out which arrangement you have. If the heating is also off, the fault may be wider than the hot-water side. If radiators work normally but taps stay cold, that points the investigation in a different direction.
Check whether the problem affects every hot tap
Try more than one outlet. One cold 'hot' tap can be a local tap or mixer problem, whereas every hot tap being affected suggests the issue is at the boiler, cylinder or shared pipework. With a combi boiler, see whether the display shows a fault code and whether the pressure gauge is in its normal range. Do not remove the boiler casing or attempt gas work. On a cylinder system, check the controls and programmer settings before assuming the cylinder itself has failed.
Cylinder systems have their own clues
If an immersion heater is fitted, it may provide a temporary alternative when the boiler is not heating the cylinder, but only use controls you already understand. A failed motorised valve, thermostat or circulation problem can leave the radiators warm while the cylinder remains cold. If the hot water runs warm for a short time and then quickly turns cold, the pattern is different from having no heat at all. The amount of stored water and the recovery time can help narrow down what is happening.
Combi boilers behave differently
A combi boiler normally detects hot-water demand when a tap opens. If the boiler does not respond, the flow sensor, controls or another internal component may be involved. If it fires but the water remains cold or fluctuates, the cause lies elsewhere within the appliance or water path. Boiler diagnosis and gas-related work must be left to a suitably qualified engineer. A plumber can still help with external pipework, taps and valves, but the correct trade depends on where the fault is found.
What to check before arranging a visit
Look at the boiler or programmer for obvious settings and fault messages, confirm whether the central heating works and test several hot taps. Note whether the water is completely cold, merely lukewarm or alternates between hot and cold. If there has been recent work on the system, mention it. Avoid repeatedly resetting a boiler that immediately faults again; the code is useful diagnostic information. Likewise, do not assume a new thermostat or valve is needed because an online symptom list happens to mention one.
Getting the right person to quote
Describe the hot-water system when you make contact: combi boiler, stored cylinder, immersion heater or something else. Say whether heating still works and whether any fault code is showing. This helps decide whether you need a general plumber or a heating engineer with the relevant boiler qualifications. For an appliance fault, a fixed repair price may only be possible after diagnosis. For external plumbing issues, photographs and the exact symptoms may allow a clearer estimate before the visit.
Do not book the wrong trade for the fault
A loss of hot water can sit on the boundary between ordinary plumbing and specialist heating work. If the problem is a tap, external valve or pipe, a general plumber may be ideal. If the boiler itself is faulting, gas appliance work requires the appropriate competence and registration. When requesting help, give the boiler or cylinder type rather than simply asking for 'a plumber'. That reduces the chance of paying for a visit from somebody who cannot work on the failed component. If a fault code is visible, write it down exactly rather than resetting the appliance until it disappears. For cylinder systems, mention whether the immersion heater works because that information can separate the stored-water side from the boiler controls.
This page is general guidance about no hot water; the cause in an individual home still needs to be established from the actual installation.