The symptom pattern

Two different reports both land here. In the first, the machine does nothing at all when you pull the trigger — no motor sound, nothing. In the second, it starts and runs perfectly well, sometimes for a full job, and then simply stops and won’t take a restart. Owners in the second group often assume the pump or motor has failed outright, because the machine was clearly working moments before.

What’s actually happening

A K7 pulls a fair amount of current, and Kärcher builds two separate protections into it that both look like “it’s broken” from the outside.

The first is a motor overload breaker. Push the machine hard for long enough — a big job, a hot day, a slightly restricted nozzle making the motor work harder than it should — and the breaker trips to protect the motor from heat damage. It needs a genuine hour to cool before it will reset, not five minutes.

The second is a voltage problem at the socket, not inside the machine. Kärcher’s own manual is specific that a weak mains supply or an extension lead causes exactly the “won’t start, motor just hums” symptom, because the motor needs a solid voltage to get spinning from a standstill even if it can run happily once turning. A long or thin extension cable drops voltage under the load of that first surge.

A damaged cable is the other case the manual calls out directly, and it’s the one that isn’t a wait-it-out fix — a cut or cracked mains lead is a safety issue on its own, regardless of what it’s doing to the pressure washer.

Working through it

Start with the checks that cost nothing. Look at the rating plate on the machine and confirm it matches your household supply — this sounds too basic to be the answer, but it’s the manual’s own first step. Then run the cable’s full length through your hands, checking for splits, kinks that have cracked the insulation, or anywhere the outer sheath has worn through.

If the machine ran and then died mid-job, that’s the overload breaker. Switch it off at the machine, walk away for a full hour, and try again cold — resetting sooner just trips it straight back out.

If it never started and instead the motor hums without turning over, unplug any extension lead and go straight into a wall socket. Kärcher also specifies a start order for this exact case: pull the trigger gun lever first, then flip the power switch to “I/ON” — not the other way round.

Only once voltage, cable and cool-down are all accounted for and the fault keeps coming back does Kärcher’s own troubleshooting stop giving you further steps and point at customer service instead.

Verdict

Worth working through in full before assuming the worst, because the overload breaker and voltage-sag causes are both completely free and between them explain most of these reports. A damaged cable or a fault that survives a proper cool-down and a direct mains connection is the genuine exception — get it looked at by an authorised centre rather than keep cycling the switch, but there’s no reason to think the machine itself is finished on the strength of this symptom alone.