No hot water but the boiler is working

When the heating is working — radiators warm up, the boiler is firing, no fault codes showing — but the hot taps run cold or lukewarm, the instinct is to assume the boiler has failed. Often it has not; the fault is somewhere else in the system that only affects hot water.

Combi boilers: usually a diverter valve or a sensor

In a combi system, hot water and heating are produced by the same boiler but routed by a diverter valve that switches between the two. If that valve sticks, or a temperature sensor on the hot water side fails, you can get heating with no hot water even though the boiler itself is fine. This is a common, well-understood fault rather than a sign the boiler needs replacing.

System and heat-only boilers: check the cylinder

If your home has a hot water cylinder rather than a combi, the boiler heating the radiators does not automatically mean hot water is being produced — that depends on the cylinder's own heating cycle and immersion element. A failed cylinder thermostat, a stuck valve, or an immersion heater that has tripped can all cause exactly this pattern. See hot water cylinders for how these systems work.

What is worth checking yourself first

• Confirm the boiler is actually set to provide hot water, not just heating — some controls let you turn one off independently.
• Check whether any other taps in the house have hot water; if only one does not, the fault is local to that tap or its pipework, not the boiler.
• Look for an error code on the boiler display, which usually points straight at the cause.

If none of that explains it, this is a boiler repair job rather than a full replacement in most cases — the parts involved are specific and fixable, not a sign the whole unit is at the end of its life.