Pressostat for a gas boiler: design and purpose + main pressostat malfunctions and ways to eliminate them

The pressure switch in the design of a gas boiler is a device that is not familiar to every owner of gas equipment. The mechanism, which is essentially a differential pressure switch, is triggered by the draft force of the flue stream generated by the fan system. But how is the pressure switch for a gas boiler arranged, why is it needed and what malfunctions is it susceptible to?

We will consider these issues in more detail in our article - let's talk about the design features of this part, which plays the role of a controller for the normal operation of the fan and the flue gas removal system. A technical analysis of the pressure switch will help to understand the operation of the gas burner, fully master the operation of the boiler, and correctly respond to emergency shutdowns.

Gas boiler pressure switch design

The execution of the pressure switch does not differ in pronounced mechanical or electrical complexity. However, the pressure switch device of a domestic gas boiler still has unique details, for example, a sensitive membrane.

This element is associated with a microswitch that acts as a signal switch. For operation on the burner control, a group of three contacts is usually used (control in normal mode or emergency mode). Basically, one contact is “shared”.

The normal operation of the boiler equipment is accompanied by a working condition thermostatic membrane, in which a closed circuit remains through one contact configuration boiler pressure switch. If the operating mode of the equipment is violated (the smoke flow changes its characteristic), the position of the sensitive membrane changes accordingly.

In this state, the working group of contacts of the microswitch breaks, while the second group (emergency switching on), on the contrary, forms a conducting circuit. This circuit supplies power to the automatic lockout system, which activates the emergency control of the gas burner as well as the water circulation system.

Thanks to the presence of a pressure switch, the following are effectively carried out:

• temperature control;
• smoke pressure monitoring;
• control condensation.

All the marked functions radically affect the operation of water heating equipment, provide not only effective functionality, but also boiler operation safety.

How can I check the functionality of the device?

Diagnostics of the proper functioning of the pressure switch of gas equipment is a necessary and useful business. As a rule, such verification is carried out by representatives of gas companies using special devices.

However, the owner of the gas boiler can also perform a kind of "testing" with simple steps. Just keep in mind - such actions violate service rules gas equipment.

If, nevertheless, the owner decides to break the rules, it is enough to reduce the supply of network water entering the boiler, for example, by partially covering the shut-off network tap of the water supply system.

As a result of a decrease in the mass of the water flow in the gas boiler system, the temperature and pressure of the flue gases inevitably begin to change. The fan increases the number of revolutions in order to create a higher vacuum in the chamber.

Accordingly, according to the theory of operation of the pressure switch, this device works, turning off the boiler due to insufficient vacuum through the supply line of silicone pipes. The device operates in the opposite case, when the vacuum value exceeds the set value.

Pressostat breakdowns and repair tips

Before considering how you can independently correct a pressure switch installed on a gas boiler, we will deal with typical malfunctions affecting this structural element.

Identifying major faults

As the practice of operating household gas boilers shows, defects in the differential relay are usually indicated by:

• the absence of a characteristic "click" when starting the fan of the exhaust gas system;
• impossibility of starting gas equipment into operation;
• error signal output through the indicator or on the display;

Any of the noted errors may be related to defects in pressure switch elements, as well as with such a rather ordinary moment as the appearance of an oxide film on contacts pressure switch microswitch.

Also, a fairly common reason for the inoperability of gas equipment is physical wear of the diaphragm of the differential relaye. This part of the device is traditionally made on the basis of silicone rubber.

With long-term use, rubber partially loses its elastic properties (dries up). As a result, an incorrect operation of the mode microswitch is noted.

Among other things, the physical fan wear flue gas discharge can cause emergency operation of the pressure switch. Similar conditions are not excluded for the reason clogging of the condensate collection system, damage to system piping and etc.

We also recommend that you familiarize yourself with the instructions for checking the functionality thrust sensor and three-way valve in a gas boiler.

How to repair a pressure switch on a gas boiler?

If the reasons for the malfunction of the pressure switch of a domestic gas boiler are specifically determined, then most often the best way out of the situation is its complete replacement.

This approach is explained by the fact that most of the differential relays of gas boilers have a "cast" design. Accordingly, repairing this kind of device will simply be more expensive than buying a new one.

However, if you have the desire, skills and capabilities, the attempt is not torture. You will first have to dismantle the device by turning off the power supply to the gas boiler and shutting off the linear gas supply valve.

Then you can start removing the pressure switch, for which you have to:

• open the boiler drum;
• remove the air intake cover;
• disconnect the silicone tube from the fan union;
• unscrew the fasteners and dismantle the pressure switch;
• disconnect a pair of faston contacts from the device;
• disconnect the silicone tube from the device connection.

The first step is to check all the silicone tubes included in the system for contamination. If there is contamination inside the tubes, it is accordingly necessary to rinse and blow out the inner area.

It is also recommended to flush and purge the inner area of ​​the differential relay using special technical fluids that are neutral to silicone.

Then the microswitch is subject to verification, namely the contact group of this element. The conductivity of the contacts is checked using a measuring device - a tester. In case of failure of conductivity on any of the contact groups, the microswitch should be repaired or replaced with a new one.

When checking the microswitch of the gas boiler pressure switch, it may be necessary to simulate a vacuum pressure. To do this, it is enough to connect a small piece of silicone tube to the pressure switch of the gas boiler, marked with a minus sign. The second ("positive" pipe) is simply closed, and through the connected pipe, air is sucked in by the mouth with little effort.

In the process of performing such manipulations, a measuring tester is connected to the contact groups of the microswitch and the presence or absence of current flow through the contacts is monitored.

This testing technique, of course, is purely "everyday" in nature. Professionally, the same actions are performed using service equipment.

In addition to a breakdown of the pressure switch, the user of a gas boiler may encounter a number of other breakdowns. We have provided an overview of popular faults and recommendations for their repair in next article.

Conclusions and useful video on the topic

In the video below, in detail about the repair of the boiler pressure switch:

It is quite possible for the user to carry out the operation of the differential relay of a gas boiler independently, using special service terminals for these actions. Almost every model of equipment has such - fittings for connecting a device that measures vacuum.

At the same time, it is strictly forbidden to carry out any technical work on gas boilers or water heaters without the appropriate permission and admission of special services. Failure to comply with such rules and requirements threatens to turn into accidents, which has been confirmed more than once by practice.

Would you like to share your experience in detecting a pressure switch malfunction and successful elimination? Or do you still have questions that we did not consider in the framework of our publication? Ask our experts and other site visitors - the feedback block is located below the article.