The Pressure Switch on My Furnace Keeps Tripping

Low Flow

• A pressure switch will continue to trip if it keeps detecting a low flow of fluid. In boilers, this means that the burners might overheat the tank and cause damage if the system isn't turned off. In heat pumps, the pressure switch will activate if the refrigerant is low. Low flow in boilers is commonly caused by a pumping issue, so examine your plumbing and pump for problems. In heat pumps low flow is a sign of a refrigerant leak somewhere in your line that must be repaired.

High Flow

• Pressure switches will also activate if they detect a high flow of fluid which is raising the pressure beyond safe levels. This is a rarer occurrence than low pressure issues, but it can happen if pumping motors are suddenly changed. It may also occur in a heat pump if too much refrigerant is added to the system. Adjusting speeds or refrigerant levels can fix this problem and keep it from occurring again.

Valves

• If flow is not an issue at its source but the pressure switch keeps tripping, you might have a stuck valve in your furnace system. If valves become jammed or fail, they can remain closed or only partially open. When this occurs your system will attempt to run but then shut off after a few minutes because it doesn't detect enough pressure. You can work back through your system and test the valves, or hire a professional to take a look at your system.

Blockages

• If your valves are working properly, the other cause of a pressure switch issue is often a blockage somewhere in your system. Dirt and debris may have entered your lines and created a clog that's preventing proper flow. This may be more common with furnaces that use gas or oil, since these fuels can create soot and may bring in contaminants with them.