Steam boiler firing even when thermostats are off

dmcs

Hi, I have a steam system with radiant and hot water loops conneected to a flat plate heat exchanger. I have separate thermostats for (1) the steam radiators throughout the house (call it the Main thermostat), (2) the radiant loops in the kitchen and (3) the hot water baseboard in the sunroom. On a few occasions, the boiler has made steam even though the thermostats are off.
I *think* this may be due to the fact that the cable for the main thermostat is in the same wall bay as a line voltage cable. If I jiggle/rearrange the low voltage cable, the boiler stops firing. If it gets moved again, the problem recurs. The line and low votage cables are several inches apart, and it would be difficult to completely separate them.
My questions: Does it make any sense that interference from the line voltage could be the cause? How far apart would they have to be to eliminate the interference? Is there a shielded cable I should use (specifically for thermostats or maybe cat 5)? Or Is there a way to effectively shield the thermostat cable (e.g run it through greenfield conduit)? Thanks!

pecmsg

If the controls are communicating then shielded cables should be used to prevent interference. For simple on / off control ,no.

Fred

There is more likely to be a short in the low voltage wiring or at the terminal connections at the thermostat.