Weil McLain sensor issues and "None" status

eugd

Going to replace my two supply and return sensors on the ultra 155 series 3 boiler. Do I need to use a sealant or just screw them in. Was getting errors on both sensors and now they just say none instead of giving a temp?

eugd

Temp menu

eugd

so I changed the sensors and the return still says its missing. first I thought that the sensor was defective so I got another one and still says "none" on the status under the temp menu. the boiler is working for heat demand but still getting a lot of post purges?

the boiler is a weil mclain ultra 155 boiler? what do I need to change the the U control module? or something else? thanks for all your help.

eugd

Anyone?

eugd

Update changed white the top sensor on the piping and now the return sensor is registering.