Oil-Fired Furnace Pressure Drops to Zero When Water Make-Up Valve Is Closed

Locate the water make-up valve, which may be indicated as the pressure-release valve in the furnace owner or installation manual, on the base or inside the control panel of the furnace. The valve looks like a metal dome, similar in shape to a fire hydrant.

Check the valve for loose connections and tighten as necessary with a wrench or pliers.

Look around the valve for signs of leaks, which may indicate that the valve is broken or damaged and needs to be replaced. Inspect the valve packing and replace if the packing seems worn or damaged. Replacement valves and packing can be purchased through the furnace manufacturer or many hardware or home-improvement stores.

Remove the black plastic cap on top of the pressure adjustment screw, which is located on top of the water make-up valve. Loosen the lock nut counterclockwise and then turn the adjustment screw clockwise to increase the set pressure of the water make-up control. Only make quarter-turn adjustments at one time. Set the pressure to 12 pounds per square inch (psi) for best results.

Inspect the valve wiring for loose or frayed wiring and contact the furnace manufacturer or another qualified service professional for assistance if there is a problem with the wiring. Do not operate the furnace until the wiring issue has been resolved, as this may present a safety hazard.