Boiler displays LOP or Low Pressure; unit will not fire or shuts down.

Safety first: Hot water under pressure can cause burns. Allow the system to cool before adding water or opening any valves. Do not exceed the boiler's rated pressure.

• Read the pressure gauge: On the Laars boiler front panel or near the piping, check the system pressure. For most residential systems, cold pressure should be around 12–20 psi.
• Look for leaks: Inspect around the boiler, near the Laars heat exchanger, circulator flanges, relief valve discharge pipe, and visible piping for signs of water leakage.
• Check the fill valve: If your system has an automatic fill (pressure reducing) valve, ensure the manual shutoff to it is open. If the system is low, the fill valve may be stuck or misadjusted and may need service.
• Manual filling (if trained): Some systems allow manual filling via a valve. If you are familiar with the procedure, slowly add water while monitoring the gauge, stopping at the recommended pressure. Bleed air from radiators or air vents as needed.
• Reset the boiler: Once proper pressure is restored, reset the control and observe operation.

When to call a professional: If pressure continues to drop, or if you are not comfortable filling and bleeding the system, contact a heating professional. A faulty expansion tank or hidden leak may be present.