The low gas pressure switch protects the burner when the available pressure drops below a safe limit. If the pressure is insufficient, combustion can become unstable or the burner may fail to start correctly.
How it works
Inside the pressostat, there is a membrane and a contact mechanism. Gas pressure moves the membrane. When the pressure is above the set limit, the electrical contact allows operation. If it falls below the limit, the contact changes state and the automation stops or prevents startup.
Where it is located
Usually, the low pressure switch is located on the gas train, at a point where it can verify that there is sufficient pressure before the valves open or before an ignition command is given.
What a low gas pressure alarm means
It does not necessarily mean that the pressostat has failed. There may actually be low network pressure, a closed valve, a clogged filter, a regulator problem, or high instantaneous consumption.
Setting
The set value is not chosen arbitrarily. It must be based on the requirements of the burner, the gas train, and the manufacturer. If set too high, unnecessary trips may be generated. If set too low, protection is reduced.
Diagnosis
A correct diagnosis starts with measuring the actual pressure using an appropriate instrument. Then, the pressure is compared with the setpoint, and it is checked whether the electrical contact changes state at the correct point.
Common causes of problems
The most common are low network pressure, pressure drop during startup, clogged filter, incorrect setting, membrane failure, or poor electrical contact.
Never permanently bridge the pressostat to make the burner operate. The device is part of the safety chain.
