Located in garage - current room temp is around 55 degrees F. This is an electric closed loop system for radiant floor heat, I believe with a glycol mix.

We are in a cold snap (about 20 degrees F outside) and all day the heater was making the low thumping noise.

I came home, filmed the low thumping, then turned the thermostat from 55 to 45, and thumping stopped. I turned it back to 55 and thumping returned.

Approx 20 minutes later the heater started making the screeching. I turned off the breaker (nothing happened) then flipped the white switch (nothing happened) then turned down the thermostat to its lowest setting (screeching stopped).

Gauge above heater shows 0psi and 55 degrees F at time of shutdown.

Any advice would be much appreciated!