When an HDS machine makes pressure normally but refuses to heat, the fault is somewhere in the burner sequence. The useful clues are what happens when heat is selected, whether the fan starts and what comes from the exhaust.
Start with the exact symptom
A machine that produces no smoke at all is different from one producing unburnt white smoke. No smoke can mean the burner has not been asked to run, the interlock chain is open or fuel is not reaching the nozzle. White smoke usually means fuel is entering but not burning correctly. Heavy dark smoke points more towards poor combustion, restricted air or incorrect fuel delivery.
Checks that do not involve guessing
- Confirm the machine has stable water pressure and recognises flow when the trigger is open.
- Check the fuel level, fuel filter and visible pipework for air leaks.
- Listen for the burner fan, ignition and fuel-solenoid sequence.
- Inspect the burner nozzle and electrodes only when the machine is isolated and cool.
- Note whether the fault changes with the temperature control or steam setting.
Why random parts waste money
The thermostat, flow switch, fuel-level switch, control supply, solenoid, ignition transformer and burner assembly all affect the same outcome. Replacing the solenoid because it clicks—or the igniter because it does not—can miss an earlier safety interlock. A proper diagnosis follows the control sequence and confirms where the signal stops.
When to stop using it
Stop if fuel is leaking, smoke continues after shutdown, the machine repeatedly trips power or the boiler becomes unusually hot. Tell the repairer the smoke colour, when it appears and which burner sounds you can hear. Those details are far more useful than simply saying “no heat”.
Send the model and symptoms, or ask us to help match a machine to the work.