Thermal runaway after replacing thermistor and heater block

I have a Mk 3 that was bought assembled and a MK 2S kit that I assembled. The MK 3 printed perfectly for aver 160 hours and then started having thermal runaways at varying times of the print. I contacted tech support at PRUSA and they sent me a new heater block, thermistor and PSU which I replaced. The printer still has the problem. I have printed with ABS, PLA, fan on and fan off. Set the fan speed to 200 as instructed by the factory technician and I'm still getting thermal runaways. I have sent pictures of the hot end where I installed the heater and thermistor and the technician said they are installed correctly.

The runaway happens at varying times into the print. I have checked the voltage at the board to the heater block wires and am getting a zero reading whilst the thermistor is still registering the temperature dropping and the hot end is cooling down after the thermal runaway. When the hot end is heating up and when it has reached operating temp the power to the heater block is fluctuating up to the 24 volts depending on whether it is heating up or not.

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Hi Mark,

please contact our support team again, I'm sure they will figure out the part, which is causing the thermal runaway.

In case you want to discuss it with the community I suggest posting on our forum, in the MK3 section:

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Mark Phillips will be eternally grateful.
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