How do you fill a slant fin boiler - Heating & Cooling

The boiler should have a make-up water connection from the home cold water supply line. Depending on when it was installed it will have a back flow preventer in line before the pressure reducing valve. The pressure reducing valve is designed to fill the boiler if the water pressure in the boiler falls below a specific set point, usually 12-15 pounds. I will be piped to the return side of the boiler in most cases. If the boiler is not filling the PRV could be defective, or depending on the specific controls, there could be a low water float assembly, either electronic or mechanical that activates a control valve to fill the boiler and that may be either stuck or defective. Boilers should be properly maintained at a minimum of every other year, once a year is best to ensure that you get 25+ years of operation from them.