Your boiler is obviously not the issue because your DHW is working. There are really only two other major components to a hydronic heating system: the circulator pump and the zone valves.
Circulator Pump
Is the circulator pump running?
If no, then check the circuit that the pump is plugged into. I see a GFCI. make sure that is not tripped and reset if necessary.
If yes, then move on to the control system and zone valves. If you have a multimeter, check voltage between the two terminals on the transformer. I suspect your transformer is OK because I see the LED on your relay is lit.
I will say that 9 out of 10 times when I've been called to troubleshoot a hydronic system, the circulator pump has been shut off, either by an electrical fault or control fault. Your controls appear (I'm just guessing because I see the lit LED on your pump relay) to be working OK so I would look closely at the pump and its electrical supply.
Zone Valves
The zone valves are commanded to open or close by applying voltage across a solenoid. This then opens the valve, allowing the circulating fluid to pass through that portion of the hydronic loop.
If the zone valves are not opening, these are the possible causes:
- The control system isn't powered up. Check the transformer and control system.
- The zone isn't calling for heat. Check the thermostat(s).
- The controls are up and zone is calling for heat, but the zone valve is dead. Check for disconnected/loose wiring between control and valve, or check the valve itself.
Edit: Thanks for adding the pictures of the zone valves. I notice that there is what appears to be a fuse in the bottom corner with a rating of 125/250V which means that your zone valves could be line volt even though I suspect they are 24V. That just means be careful around them (although you already should be with any power, of course).
Those syncho motors should be audible when the open and close. Try powering the system off and on and see if you can hear one or both of those valves working.
Controls
Thanks for also adding a pic of the controls. I see that there is really only one signal wire (yellow) which suggests that the decision for which zone to open is being made at the thermostats themselves and the control board is just responsible for a general call for heating. If the zone valves are not working, I suggest looking at the thermostats themselves to verify they are working properly.
... One more thing...
There is one other potential issue and that is air bubbles. Since air compresses at a different rate than water or glycol or whatever is in the pipes, an air bubble at a high spot can block the flow enough that even though your zone valve is open and your pump is working, it can't push that air bubble back down and out of the system, effectively shutting off the zone.
If the pressure in the system was low due to a leak and any air got in, the air would make its way to the highest point and make that blocking bubble. Taking another look at the pressure gauge pictured below your boiler, that pressure looks low to me. I usually see at least 20-30 psi. There is an expansion tank that takes up some of the slack, but it can also leak, either externally or internally (the air bladder inside) so if everything on the control side tests out OK, that would be where I'd focus.
hydronic baseboard heating loops