Curiously, I turned it on auto this afternoon thinking to toggle it into manual and I could see and hear a sizzle at that element relay when I switched it into manual.  I so I left it in auto and observed.  It is holding a steady normal temp and pressure currently several hours running.  Did I weld something back together?  lol.  I have a pro arriving tomorrow.

Even if I could find out the part number for that relay, find one, replace it, and test it, there still could be another cascaded error.  And meanwhile my wife will be taking cold showers and my real work will be on hold.  Sooooo......

I called the landlord.  They will cover the cost of getting a professional to finish the job. 

In the meantime I wonder if I can run this on manual mode if I put the card back in even though that relay (and who knows what else) is bad.

Thanks to everyone that had a read, and thanks to Carl for the reply!

I just found 8 MOC3062 triac/optocouplers in my spare parts.  They seem to be functionally equivalent (just can take higher voltage) so I plan to replace them all now and see if my problem is the same as in the link I posted above.  Unfortunately I don't have any compatible relays on hand.

I can read Swedish so all comments appreciated!

Executive summary (tl;dr):  GT3 (hot water temperature) goes to about 90C... almost boiling tap water.  There seems to be no way to set this temperature.

Question:  How do I control the varmvattentemperaturen?
{edit: found this post

Problem was a bad triac on a controller board.  Sound like my problem?
}

The details: I live in a rented house with an IVT 290, no heat pump.  The IVT received no maintenance for many years... seemed to work fine but every now and then I would have to reset the fuse on the bottom of the control panel.  A couple weeks ago it started to require a reset every day so I figured something was wrong.

What I've done:

Avluftning.  I went around to every radiator in the house and bled the air.  A couple of them had quite a lot.  I also bled the tank in the heater until water came out.  (using the valve next to the pressure relief valve/hose marked 2.5atm pressure.  the tank had a lot of air in it.)

Filling.  I opened the supply valve on the bottom left while avluftning to add water to the heating system.  Once the system was running and warm, I adjusted that valve again until the pressure in the system was around 1.5atm.

The system seemed to operate better now (not blowing the breaker) but the tap water in the house was really warm, close to 80C!  This causes the pressure in the heating system to go up also... above the stated max pressure of 2.5atm.

I cannot run the system now without GT3 going to max.