1. Check the boiler display
An error code on the display is the biggest clue there is. Note it down exactly before resetting anything, and tell us the code when you call. One press of the reset button is fine; repeatedly resetting a boiler that keeps locking out can make a fault worse.
2. Check the pressure
If the gauge reads below about 0.5 bar, the boiler will refuse to heat water. Topping it up takes five minutes: see our guide to repressurising the boiler.
3. Check the controls
It sounds obvious, but timers and thermostats cause a surprising share of "no hot water" calls. Check the programmer has hot water switched on and the schedule has not been changed, check the cylinder thermostat if you have one, and check room stats or smart controls have working batteries. After a power cut, some programmers reset to defaults.
4. In winter: the condensate pipe
Modern condensing boilers drain a small amount of water through a plastic pipe, often running outside to a drain. In freezing weather that pipe can ice up, and the boiler shuts down, typically with a specific error code and a gurgling sound. If you can reach the pipe safely at ground level, thawing it with warm (never boiling) water poured along the pipe, or a hot water bottle held against it, will often bring the boiler straight back. If it keeps happening, the pipe run needs insulating or rerouting, which is a small job for us.
5. Heating works but hot water does not?
If the radiators heat up fine but taps run cold, or the other way round, that usually points to the diverter valve on a combi, or the motorised valve or cylinder on a conventional system. Those are engineer jobs, but they are common, well-understood repairs. One of our reviews is from exactly this kind of job: a cylinder, pipes and valves replaced when they had had their day.
When to stop and call
If the checks above have not restored your hot water, the fault is inside the boiler or the system, and that is where DIY must stop. Never open the boiler casing: gas appliance work is illegal unless Gas Safe registered. Call us on 07496 925309, tell us the error code and what you have tried, and we will give you an honest diagnosis with a fixed price agreed before any repair. See boiler and heating repairs for how it works.