Published at Tuesday, March 26th, 2019 - 23:47:03 PM. wiring. By Pierrette Poulain.
The next control is the pressure control. The pressure control is a switch that, when working as a high-limit safety, opens on pressure rise. The switch can be either a micro switch or a mercury switch. The pressure control is wired in series with the LWCO, the rollout switch, and the spill switch. There are a few things to remember about pressure controls. First, the cut-out pressure should never be set higher than 2 psi. This is plenty of pressure for most residential one-pipe gravity systems. Higher pressures are inviting problems.
One time I had a buddy with 90 “defective” boilers; this was the guy who forgot to check the gas meters. The next time he called me he had 265 defective boilers. Of course, my first question was, “Do you have gas?” After I got called some nasty names, we proceeded with the questioning. I asked him if he had 110 V to terminal L1 and L2. This is always our starting point, making sure the electricity is turned on. I got the classic answer: “How do I know, I’m only a plumber.” I asked to speak to the electrician, who confirmed that he had power to L1 and L2. I asked what the voltage was; sometimes you have lower voltage and the system won’t work. He confirmed that he had 120 V. Next, I asked him if he had continuity through the control circuit. His answer was, “I’m a union electrician, I put power to the boiler and hook up thermostats; I don’t know about boiler wiring.” It was time for a field visit.
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