Diagnostics and repair of boiler pressure switch

1. Purpose of the pressure switch. 2. The principle of operation. 3. Symptoms of malfunction. 4. Causes of failure. 5. Diagnostics and repair of the boiler's pressure switch.

Purpose of the pressure switch.

The pressure switch, also known as the smoke pressure switch, differential switch, smoke sensor is a sensitive device designed to turn off the boiler in case of poor removal of spent fuel. It controls the operation of the fan and in case of insufficient flow of polluted air in the chimney sends a signal to the control board to turn off gas burners. These sensors are equipped with gas water heaters with a forced smoke exhaust system.

Principle of operation.

Pressostat of a gas boiler consists of a body with nozzles, a microswitch in 2 positions, a moving diaphragm with a pin, which divides the internal space of the body into 2 chambers.
Diagnosis and repair of the boiler pressure switch
When the smoke exhauster does not workpins 1, 2 are in the closed position (pin 2 is not connected to the control board). When starting the fan in chamber 2, a vacuum occurs, which is transmitted from the rotation of the turbine through the Venturi tube, tube with condensate collector and pipe 2, due to which the diaphragm with the pin attracts and closes contacts 1, 3 (contacts 1, 2 are open). This signal, about the normal operation of the exhauster, goes to the control board (contacts 1, 3 are connected to the control module), which ensures the operation of the boiler according to a given algorithm.


In the event of a breakdown The smoke detector has the following symptom symptoms: 1. In the differential relay, when the fan is turned on, there is no click of the microswitch. 2. The boiler does not work, and gives an error like this: “Pnevmorele is turned off, the fan is working.”

Causes of breakdown.

The following reasons can cause breakage or malfunction of the relay: 1. Contact oxidation. At the start of the fan operation, the microswitch is clicked, but because of the oxidized film on its conductive parts, the circuit does not close. 2. Wear of membrane material. The deterioration of the technical properties of the moving body of the smoke sensor contributes to the disruption of its operation. 3.Clogging, damage or formation of a septum in a tube with a kandensat collector. When cracks, tears form on this element, as well as if the tube is clogged or the device is filled with water, the sensor does not adequately respond to changes. 4. Reduced fan performance. The pulling forces arising from the discharge in the turbine chamber are insufficient to move the diaphragm to the microswitch.

Diagnostics and repair of the boiler pressostat.

To identify a faulty unit, you can proceed as follows: - turn off and de-energize the boiler; - open the front of the housing; - connect the contact 1, 3; - reset the error and start the boiler. If the boiler starts working, it means that the failure is in the pressure switch . To diagnose and repair it, it is necessary to investigate the condition of the following elements: 1. Tubes condensate. It is inspected for the presence of thermal wear and filling the internal cavity with dirt and condensate. The tube is placed in an environment of high temperatures. From thermal radiation, the material of the tube loses its physical properties or is covered by through cracks.Also, its channels can be clogged with dirt or filled with water, which is formed due to sudden temperature changes between the environment and hot exhaust gases. If you find defective areas, you must replace the handset with a new one, or try to repair the worn product yourself.
 Diagnostics and repair of the boiler pressure switch
For example, deep cracks on the cylindrical surface can be insulated with temperature-resistant material (tape, aluminum tape). 2. Internal camera smoke detector. When moisture enters the inside of the case, the contacts of the microswitch begin to oxidize rapidly. Therefore, if condensate is constantly present in the relay, especially this process is pronounced at negative temperatures, it is advisable to move the pressostat of the gas boiler to another place, away from the cold wall of the inlet channel.
Diagnostics and repair of the boiler pressure switch
3. Electrical contacts.Connect the multimeter to pins 1 and 3 in the diode test mode.
 Diagnostics and repair of boiler pressostat
Using a mouth, create a vacuum in the chamber of smoke detector № 2. If the tester wilts or shows a short circuit, which means that the conductive parts of the relay are not oxidized if the display shows a unit, hence they are faulty. Many models of the smoke pressure switch are enclosed in a one-piece case, so it will be problematic to inspect the condition of the contacts. Since the halves of the plastic housing are connected together by soldering, therefore, to disconnect it, you must carefully clean the fused places. After opening, clean the conductive parts, inspect the membrane for defects and, in the absence of significant damage in the reverse order, assemble the repaired device. If you decide to replace it, then you need to choose a similar model. 4. Fan power. If the power of the smoke exhaustor deteriorates, due to a decrease in mains voltage, strong contamination of the turbine blades or wear of the bearings, the diaphragm of the device will not be fully attracted to the microswitch.Although there are adjustable screws on the relay, with which you can adjust the diaphragm response range, it’s better not to touch them, since you can knock down the factory settings and then set the required position for a long time. Therefore, carefully inspect the condition of the listed elements, perhaps the breakage lies in the boiler exhaust fan. You can learn about which components may be faulty in it from the article: “Diagnostics and repair of the boiler fan”.

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