I received a comment on the last post and the point he made is important to understand. The comment was: “What you forgot was the types of regulators, pilot bleed and 100% lock up. A lot of times a contractor replaces an old unit but leaves the regulator. If the old unit had a pilot –like on a unit heater, the regulator will cause intermittent problems. Also, due to the new unit being 100% shut off, the regulator tends to try to bleed and over pressurizes the gas valve.”
Old regulators that were used on units with standing pilots, those regulators are not suitable for dead-end lockup service. They are capable of controlling pressure at very low flows such as standing pilots, but should not be used as a line gas pressure regulator for appliances equipped with electronic ignition unless automatic control valve can open against line pressure.. Since most valves cannot open against more than 12 IWC, these regulators will cause problems and lock-outs.
It is also important to know that regulator have temperature ratings just as gas valves do for roof top unit applications. You must use a regulator that is capable of operating down to -40 F if exposing them to the weather on a roof.
Thanks for the comment and for the suggestion about clarifying that there are different types of gas pressure regulators. Hopefully , this additional information will help solve some problems on jobs.