MAX31855 with washer thermocouple problem

[RosscoS]

I have a MAX31855 breakout board that I am using with a washer type thermocouple so that I can attach it to a boiler.

When the thermocouple is sitting in air, it reads fine, however when I attach it to the boiler, the serial display indicates a problem with the thermocouple.

I have connected the GND of the boiler to the Arduino & MAX31855 GND.
I have tried putting Mica washers between the washer and the boiler, also between the washer and the screw with zero success.

Thanks in advance for any assistance.

[adafruit_support_bill]

The MAX31855 is not compatible with grounded junction thermocouples. You need to insulate the washer from the grounded tank.

I have tried putting Mica washers between the washer and the boiler, also between the washer and the screw with zero success.

Mica washers won't prevent the screw from contacting the sides of the hole in the washer.

[Nidaybak]

It is remarkable, very much the helpful information

[RosscoS]

The MAX31855 is not compatible with grounded junction thermocouples. You need to insulate the washer from the grounded tank.

Would I be correct in saying that one alternative would be a ungrounded junction washer type thermocouple? Or am I way off?

[adafruit_support_bill]

ungrounded junction washer type thermocouple?

Yes, that should work.

[RosscoS]

A bunch of teflon tape on the screw and a few mica washers did the trick!