An HDS burner is not controlled by one simple on-off switch. The machine must have a demand for heat, sufficient water flow and the required safety signals before it runs the combustion sequence. The point at which that sequence stops is more useful than guessing a component.
1. The machine must first make stable pressure
A restricted inlet, blocked filter, trapped air or water-shortage signal can prevent burner operation even when the motor runs. Confirm an adequate water supply and stable pressure before investigating the diesel side.
2. There must be a genuine call for heat
The programme selector, temperature setting and temperature sensor determine whether heat is required. A machine already at its selected temperature will cycle the burner off normally. A faulty control or implausible sensor reading may prevent the demand from reaching the burner circuit.
3. Airflow and ignition begin the burner sequence
When the required conditions are present, the burner blower supplies combustion air and the ignition system creates the spark. Listen from a safe position and note whether the fan starts cleanly and whether an ignition sound is present. Covers and guards should remain fitted during operator-level observations.
4. Fuel must arrive in the correct condition
The fuel pump, filter, solenoid, pipework and burner nozzle all affect delivery. No smoke can mean that fuel has not reached the chamber. White smoke commonly means fuel is present but is not igniting or burning properly. Heavy dark smoke points towards poor combustion and demands immediate shutdown.
5. The flame must remain proven
Machines equipped with flame monitoring must recognise reliable combustion. A dirty viewing path, unstable flame, fuel restriction or sensor problem can make the burner light and then stop. A successful first ignition does not prove that it will restart correctly after the trigger closes.
A useful workshop test covers the complete cycle
Diagnosis should include cold start, pressure under load, heat-up, temperature control, trigger shut-off and several hot restarts. That is how intermittent flow signals, weak ignition and combustion faults are separated from normal temperature cycling.
Read the general no-heat fault guide →
Arrange hot-pressure-washer diagnosis →
Send the model and symptoms, or ask us to help match a machine to the work.