At work today, I had to rewire 4 heating system boilers in a commercial building. Three of these boilers had to run off of one thermostat, I was going to use a 3 pole control relay to accomplish this. Each of these boilers has it's own 24volt control circuit, a (R) and a (W) terminal to fire the boiler. The previous installer didn't use a relay, he joined all 3 (R) terminals together and all 3 (W) terminals together, from each boiler and put them on 1 thermostat. My thinking has always been, if you join 3 separate control systems together you would short them out, possibly burning out the transformers, but these boilers have worked like this for about a year. Is it okay to do this without a relay. Thanks for any replies.