Low system pressure: Codes, Causes & Fixes

Low system pressure is one of the most common boiler faults: in many residential hydronic systems the gauge should read around 12–15 psi when cold, and the boiler locks out when pressure drops too far. If your owner's manual explicitly describes topping up and you are comfortable doing so, follow its steps exactly; otherwise leave it to a technician. A pressure that keeps falling points to a leak, a failing pressure relief valve or an expansion tank problem, all of which need a licensed heating technician.