boiler
I need to increase the pressure to the boiler, how should I proceed? I checked on YouTube and found a couple of systems but they do not apply to my model (at least not at first sight).
Some pics here (click for full size):
This boiler also feeds the floor heating system.
The short answer: you should replace the relief valve.
The long answer: In general, you should not attempt to repair any pressure relief valve. This valve is the only over-pressure safety in the system. This should only open if there is a blockage in the system (causing a pressure buildup), or if filling the system with a faulty pressure reducing valve.
Normally these valves fail due to calcium build up on the interior, which is hard to avoid without having a water softening system installed.
I would recommend changing out both the pressure relief valve, and the pressure reducing valve, as it appears to have quite a bit of calcium build up as well (and may have a small leak). To have both replaced would generally cost in the range of $200 to $500, depending if you replaced them yourself or not. If there are no other leaks or issues with the system, changing both of these valves will solve your zero-pressure issue.
Okay... After reviewing your new photos, I think I have it figured out.
This is what your system looks like
You'll have to excuse the glitter pens, it's the only thing I could find on my wife's desk.
It's pretty simple actually. When a thermostat calls for heat, the valve for that zone opens, and the boiler is also signaled via the auxiliary switch in the valve.
To get a C wire to one or more of the thermostats, you'll simply run a wire from the other side of the transformer on the wall.
NOTE: If this diagram is accurate, the white wire to the thermostat is R, while the red wire is W.
The original wire from the transformer should be connected to the R terminal on the thermostat, while the new C wire should be connected to the C terminal on the new thermostat. This should supply power to the thermostat, and allow it to operate as normal.
The way your thermostat is currently wired, you'll have to swap the white and red wires to get it to work. So white will go to R, and red will go to W.
To make this fit a more common wiring style, I'd probably rewire it a bit. So that the red wires going to the thermostat, connected the transformer and the R terminals. And the white wires connected from the zone valves to the W terminals on the thermostats.
Rewired to fit a more common style.
Then you'll run the blue wire from the white transformer lead, up to the C terminal on the thermostat.
Best Answer
Here's the manual in Italian and Spanish1, if you can read it.
The part about pressuring is usually covered at the beginning in maintenance but more fully explained in the installation section.
1 Cheers for clarifying the language.