Pressure switch for a gas boiler: device, review of popular faults and their repair

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 activated under the influence of the draft force of the smoke flow generated by the fan system. But how does a pressure switch for a gas boiler work, why is it needed and what malfunctions are 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 you understand the operation of the gas burner, fully master the operation of the boiler, and correctly respond to emergency shutdowns.

Design of a gas boiler pressure switch

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

This element is connected to a microswitch that acts as a signal switch. To control the burner, a group of three contacts is usually used (control in normal mode or emergency mode). Essentially, one contact is "shared".

A widely used version of a differential relay designed to work in the design of many household gas boilers. It looks like a technically simple device, but significant in terms of functionality.

The normal operating mode of boiler equipment is accompanied by the operating state of the thermostatic membrane, in which the circuit remains closed through one configuration of boiler pressure switch contacts. If the operating mode of the equipment is disrupted (the smoke flow changes the characteristic), the position of the sensitive membrane changes accordingly.

In this condition, the working group of microswitch contacts is broken, while the second group (emergency switch), on the contrary, forms a conductive circuit. Through this circuit, power is supplied to the automatic locking system, as a result of which emergency control of the gas burner is activated, as well as the water circulation system.

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

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

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

How to check the functioning of the device?

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

The classic diagram for connecting a differential relay (pressostat) in the design of a domestic gas boiler: 1 – fan; 2 – manometric device; 3 – differential relay

However, the owner of the gas boiler himself can also perform a kind of “testing” with simple steps. Just keep in mind that 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 supplied to the boiler, for example, by partially closing the shut-off network tap of the water supply.

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 begins to change. The fan increases the speed to create greater vacuum in the chamber.

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

Pressostat breakdowns and repair tips

Before considering how you can independently fix 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:

• absence of a characteristic “click” when starting the exhaust system fan;
• inability to put gas equipment into operation;
• output of an error signal through an indicator or on the display;

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

In order to be able to perform high-quality cleaning of the contact petals of the microswitch, this element of the system must be dismantled. However, oxidation of the contact inside cannot be ruled out, which requires a complete replacement of the part.

Also, a fairly common cause of gas equipment failure is physical differential relay membrane weare. 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 out). As a result, incorrect operation of the mode microswitch is noted.

Among other things, physical fan wear removal of flue gases may cause emergency operation of the pressure switch. Similar conditions cannot be excluded due to clogged condensate collection system, damage to system pipelines and etc.

We also recommend that you read the instructions for checking functionality traction 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 identified, then most often the optimal way out is to completely replace it.

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

It is easy to buy a new pressure switch for a gas household boiler of one model or another in the appropriate stores. The commercial market offers devices for almost any model

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

Then you can begin to remove the pressure switch, for which you will:

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

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

It is also recommended to wash and blow out the internal area of ​​the differential relay using special technical fluids that are neutral to silicone.

It is easy to check the functionality of the microswitch of the differential relay of a gas boiler. To do this, in the resistance measurement mode, the contact groups are “ringed” for conductivity

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

When checking the pressure switch microswitch of a gas boiler, it may be necessary to simulate a vacuum pressure. To do this, just 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 air is sucked through the connected tube through the mouth with little effort.

In the process of performing such manipulations, connect a measuring tester to the contact groups of the microswitch and look for the presence or absence of current passing through the contacts.

This testing technique, of course, is exclusively of a “domestic” nature. Professionally, these 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

The video below details 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 these - fittings for connecting a device that measures vacuum.

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

Would you like to tell us about your experience in identifying a faulty pressure switch and successfully resolving it? Or do you still have questions that we did not address in our publication? Ask them to our experts and other site visitors - the feedback block is located below the article.