I noticed that often the temperature of my e61 machine drops at idle to under 214F (typical idle temperature) with the pstat setting at about 1.25bar. The temperature goes down to around 185F or even less sometimes.

My machine is a Brasilia Gabriella whose internals are very similar to an Andreja and a few other machines.

When tracing the causes I noticed that my OPV opens and you can see that some water is going up the return tube to the water tank. You can even hear a sound of the water slowly being pushed. I think this causes the thermosyphon to stall. I'm wondering why does the pressure increase inside the HX loop, I am guessing there might be a leak that creates a gap which is filled by steam causing the pressure to rise!

I don't know how to resolve this issue. Any tips or suggestions are welcome.

Thanks.