leaky zone valve on boiler?

[kitchenredo]

I do maintenance on a small apartment building. Seven apartments are heated from a single boiler, with temperature control by Taco zone valves. While painting an unoccupied apartment I noticed it was warm, even though the thermostat was turned down. I felt the baseboard heaters in several rooms and they were warm, but not as warm as when the thermostat is on. I went to the heater in the basement and felt the copper pipe leading down into the zone valve, and it did not feel warm. The pipe at an adjacent zone valve heating the apartment immediately above where I was working was quite hot. My question is, how did the empty apartment with the thermostat turned down have warm pipes in the baseboard heaters? Even though the pipe to the zone valve did not feel warm, could there be leakage through the valve?

 

[voletl]

Zone valve could be stuck open does the lever easily move up and down or is there some tension behind it

 

[fixitron]

If zone valve were stuck open, the piping would be as hot as the boiler water every time the circulator runs. If it is only lukewarm, it is more likely a sticking flow check valve, which allows thermosiphoning when any other zone calls for heat.

 

[voletl]

I've rarely seen heating systems that use zone valves have flow checks piped-in with them as well unless it's built into the circulator and if that was the case all the zones would be lukewarm not just this one

 

[frodo]

look on the zone valve
it should have a little arm sticking out, this is the manual override
you can move the arm to open the valve or cclose the valve,
it also has a notch to lock it open.
move the arm to the closed position,
see if that works, if not, move it back and forth a few times in hopes of clearing out what ever has it stuck open

if it still leaks, buy a new zone valve, this time buy a honey well because tacos are crap

 

[TomFOhio]

If the body is ok you can buy just the taco head. Very easy to replace it.