Low Hot Water Pressure on an Oil Furnace


Oil hot water boilers, or furnaces, generate hot water for a home or business and distribute the water through the pipes to the necessary faucet or appliance on demand. If the water pressure from the furnace is low, however, the water pressure for the faucets and appliances will be low as well, which can create several problems.

Older Models

  • Many older oil water furnaces have a bell-like device that opens and adds water into the boiler when the water pressure inside the tank falls below typical levels, around 12 pounds per square inch. If the water pressure is too low and the water feeder valve is not adding water as expected to increase the water pressure, you can adjust the screw and lock nut location on top of the valve. Turn the screw and lock nut clockwise to increase the overall pressure but perform only one-quarter turns at a time to slowly increase the water pressure.

Newer Models

  • Newer boilers have what is called a pressure-reducing valve, also known as an automatic water feeder, which is also bell-shaped. This device is meant to reduce the overall water pressure, especially in tall buildings where the water pressure may be higher than the typical 12 psi. The water feed valve should automatically add water to the system if the pressure drops below 12 psi, so if the water pressure is below 12 psi and the automatic water feed valve is not adding water, contact the furnace manufacturer for assistance, as the valve may be broken or defective.

Water Supply Valve

  • Check the water supply valve on the oil furnace for dirt, debris or other obstructions that may be limiting water flow from the unit, thereby affecting the water pressure. Clean the valve and make sure it is set in the open position.


  • Another factor that may restrict water flow and pressure is the buildup of sediment in the oil boiler. This often happens over time. The problem can often be corrected by draining the water tank to remove the sediment and refilling the boiler. Turn off the oil furnace, close the water supply valve and let the unit cool completely. Place a very large bucket under the purge valve and open the valve to let the tank drain thoroughly. Blow air through the hose carefully if the water stops draining due to a vapor lock. Let the tank drain completely and close the purge valve. Open the water supply valve and restore power to the boiler.

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