No hot water does not always mean the oil boiler itself has failed. The problem can sit with controls, the hot water cylinder, a valve, the oil burner, or the oil supply.

Key points

  • Check simple controls before assuming a major fault.
  • Only reset the burner once if it is locked out and there are no unsafe signs.
  • Stop and call if there is oil smell, smoke, leaking oil or repeated lockout.
  • A proper fault check avoids guessing at parts.

Quick checks before calling

Check the programmer, room thermostat, cylinder thermostat, fused spur, oil level and any visible lockout light. If the central heating is working but the hot water is not, the boiler may not be the only suspect.

On many homes the oil boiler heats a hot water cylinder. A motorised valve, timer setting or cylinder thermostat can stop hot water even when the boiler itself is able to run.

If the boiler is locked out

A red or illuminated reset button usually means the burner has tried to start and stopped for safety. If there is no smell of oil, smoke, unusual noise or leak, one reset may be reasonable.

If it locks out again, leave it off. Repeated resets can make a fault worse and may put unburnt oil into the combustion chamber.

Common causes

No hot water can be caused by oil supply issues, a blocked filter, failed ignition, photocell problems, a worn nozzle, poor combustion, controls, pumps or valves.

The useful first step is diagnosis. The symptom tells you where to start looking, but it does not prove which part has failed.

What an engineer checks

A fault visit normally starts with the history of the fault, visible safety checks, controls, oil supply, burner operation and combustion condition where the appliance can be run safely.

Once the cause is understood, the repair can be explained clearly before further work is agreed.

Common questions

Should I press the reset button?

Press it once only if there is no smell of oil, smoke, leak or unusual noise. If it locks out again, leave it off and arrange a fault check.

Can no hot water be a controls fault?

Yes. On stored hot water systems the timer, cylinder thermostat or motorised valve can stop hot water even if the boiler is not the root cause.