Hotend wil not stay on

I am commissioning a large delta printer I have fitted an X5 mini Everything is working except the nozzle heater. When I try to switch it on in the pronterface screen the graph indicates that it is switching on for a second of two and then back off. The heat bed works fine. I checked that the hot end thermistor was OK by removing it from the hot end and placing it on the heat bed, It tracked the heat bed thermistor perfectly. I ran the auto-tune routine and it cycled through it very quickly (the nozzle did not heat up) so how could it produce a result without an actual heat cycle? yet it produced a set of PID values.
I can see what is going on but do not know why or how to fix it.
What have I missed?

Imported from wikidot

What does M105 say, both when heating, and when not heating ?

It shows current temp from the thermistor, set temp and then the set temp goes back to zero. I took a screen shot of the prontiface screen but do not know how to include it.

Can you just copy/paste, or manually copy, the text ?

It is just a screen shot of the spike in the graph where it turns on then straight back off

I get the feeling that something in the software is shutting it back off as soon as it is turned on. Can you give me some idea of what I could have set wrong to cause that. I downloaded a fresh copy of the bin file in case it had got messed up but no change. I assume it is a setting I have got wrong or overlooked as there are plenty of other people using it with no problems.

I really need you to type here the result of sending M105, when powered off, and when powered on.

Bellow is a cut and paste of sennding M105 with power off and then power back on. There was no resopnse to M105 with power on.

Can’t write to printer (disconnected?) (SerialException): Write timeout
Disconnecting after 4 failed writes.
Disconnected.

Printer is not online.
Connecting…
Printer is now online.

SENDING:M105

I meant, “with heating on” when I said “with power on” ( ie. “power to the heater” ).

Send : 
M104 S0
M105
M104 S200
M105

If pronterface does not display the returned value, try sending @M105, or using something like cutecom to send the commands. But I need the returned values.

If there is an intermittent open in the thermistor circuit the firmware will turn the heater off.

I built my own hot end and first put in a thermistor called a PT100 but could not find and config setup that would work for it so went back to the electronics wholesaler and go a 100K thermistor that seems to work perfectly with the default epoc settings. I can remove it from the hot end and place it on the heat bed and it will track the heat bed thermistor exactly. However I will check out the wiring in the morning as I am not prepared to knock any suggestion.
I am however still somewhat fixated on the software idea because when I turn the nozzle on, on the screen the graph showing current temp and target temp spikes up to the target for about a second and then drops back to zero

PT100 temperature sensors need a special board to work with our 3d printer controllers. E3D sells a add on board for a PT100 to make it work. Im wondering if your PID settings would maybe have something to do with the spike. It sounds like to me you have a short somewhere in the line possibly causing it to spike and maybe trigger an overheat shutoff.

If I have a short (and anything is possible as I am big on enthusiasm and not so great on electronic knowhow) how come the display shows good temperature all the time? surely there would be something showing up here too.

Re the PID settings. I tried running the auto tune and it cycled through it very quickly and gave a set of results without actually heating up the hotend.

I tried fitting an off the shelf hot end assembly complete with heater and thermistor to test the short circuit theory and the result was just the same.

Here is the hotend part of the config file.

temperature_control.hotend.enable true # Whether to activate this ( “hotend” ) module at all. All configuration is ignored if false.

temperature_control.hotend.thermistor_pin 0.24 # Pin for the thermistor to read
temperature_control.
hotend.heater_pin 2.5 #was 2.5 Pin that controls the heater
temperature_control.
hotend.thermistor EPCOS100K #was EPCOS100K see src/modules/tools/temperaturecontrol/TemperatureControl.cpp:64 for a list of valid thermistor names

temperature_control.hotend.set_m_code 104 #
temperature_control.hotend.
set_and_wait_m_code 109 #

temperature_control.hotend.designator T #was T
#P39.98 I5.00 D79.91

#temperature_control.hotend.rt_curve 25,109.73,150,157.31,190.45 #
temperature_control.hotend.p_factor 39.98 #

temperature_control.hotend.i_factor 5.0 #

temperature_control.hotend.d_factor 79.91 #

temperature_control.hotend.max_temp 250 #
#temperature_control.hotend.max_pwm 64 #

Is this helpful?

SENDING:M104 S0

SENDING:M105
ok T:17.7 /0.0 @0 B:17.6 /0.0 @0

SENDING:M104 S200

SENDING:M105
ok T:17.5 /0.0 @0 B:17.6 /0.0 @0

SENDING:M105