Diesel karcher Hot issue

[smeato]

Calling any karcher specialists,
I have a HDS 558c, 240v with diesel burner, problem is it only runs on full heat and not cold, with burner always firing. I used to be able to regulate with temp control switch. Initially I thought thermo control switch which runs a wire with a bulb on the end that locates in a small pocket on the hot water pipe outlet. I did a test on this bulb with a heat gun and checked continuity of wiring, gently applying heat the control switch clicks and continuity stops which has me thinking it may not be this thermo switch.
Any suggestions appreciated before I outlay for a thermo switch.
Cheers

 

[carbon]

Check the internal opening on the disc that rotates the thermostat isn’t damaged. They can crack and then the thermostat doesn’t rotate completely back to the cold position

 

[JOEPRO]

@Turbo

 

[Turbo]

Fuel solenoid stuck open would be my guess.

 

[Turbo]

Follow the wiring from the stat. Power normally comes from the on off switch or contactor, through the flow switch to the stat and finally to the fuel solenoid.
Disconnect the solenoid wire and see what happens.

 

[smeato]

Hey guys, thanks for your help, did a few check and looks like fuel solenoid. Will post back once I get time to fix.
Cheers