I have a 5 zone hot water heating system. All zones work fine except for one. The zone valve opens when the thermostat goes on but the water pump and boiler don't go on. I am wondering of I need to replace the zone valve because maybe the current isn't passing through onto the pump to turn it on. Also the zone valve for this zone gets very hot. Any help would be greatly appreciated.

In the only hot water system I am familiar with, the thermostats signal the zone valve to open. When the valve is open, it closes contacts starting the boiler and pump if not already open. You need to look at how yours is wired and make sure the signal to start the boiler get to it from the zone valve. The zone valve I was working on was a White Rogers. They have some very helpful information on their website. Other brands may too.

Not sure what to say about the valve getting hot. Does it use a solenoid to open the valve, or a motor and a rotary valve?

Honeywell has a end switch that can go bad. White rodgers uses a rotary plate as a swith and it can also go bad. To test jumper or connect the two wires that go back to the control for the pump ETC. If the pump goes on you have found the problem. If this is the problem replace the valve. On most Honeywell / Whitr rodgers valves you do not have to drain the system to replace the power head assembly only. The valve body can stay installed on the pipe. If you really want to get into it you can remove and replace the entire valve but you will have to drain the system and solder in the new yalve if it is on a copper line. Good luck.

Zone valves often get very warm when actuated. It sounds like it is bad from what you've said. Just a note, you wouldn't believe how many zone valves are on the market so to make you job replacing it easier by the same model again.