In household storage boilers, a capillary thermostat is used as a temperature sensor - the device is quite unpretentious, however, in my case, after three years of operation, it died out for a long time. The search for a similar one in our area was not successful, so the question arose about an electronic regulator - as simple as possible and, if possible, reliable. I started surfing the Internet, and one of the first I came across was a well-known scheme:
In preparation for her practical implementation, I found an article on the Internet: “A simple thermostat based on an adjustable zener diode TL431,” which was accepted for implementation.
My modified version:
Differences from the original scheme:
- Thermistor – rated 22 kOhm.
- Variable resistor – 33 kOhm. Since I don't need a wide range of the regulator, I deliberately moved it towards a wider range. high temperature, receiving in return smoothness of adjustment.
- Instead of the 7805 stabilizer, it was used Russian analogue KR142EN5A.
- The manual mode toggle switch has been replaced with the KM1-1 button.
- The complete starting block is used as a load switch
- IEK KMI-22560, in the housing of which the circuit was mounted.
- Power supply 220/12V - converted from a power supply unit from Sega. I stabilized the 12-volt voltage, so to speak, with a reserve; theoretically, you can do without it. If you decide to leave it, then instead of the transistor and zener diode you can use KR142EN8B. Alas, I didn’t have it on hand.
In place of the “stop” button there is a neon indicator connected in parallel to the contacts of the intermediate relay, signaling the Standby mode. On the front side, through the hole, the KL102 LED is visible - an indicator of power supply to the control board. The SG-5 connector is used to connect 12-volt voltage and a temperature sensor.
Inside view:
A variable resistor installed on the side of the printed conductors simultaneously plays the role of a printed circuit board holder.
Now – about the temperature sensor itself. The fact is that in storage boilers there is a special sealed tube on the bottom side, approximately half the height of the tank (the actual length of the tube depends on the capacity of the boiler). It is into this that the capillary rod of the standard regulator is inserted. I did the following: I took a piece of PUNP 2x1.5 wire, 60 cm long. Having removed the outer insulation at a distance of 45 cm, I wrapped one of the wires with a thin strip of FUM, which is used in plumbing. Next, having soldered the thermistor leads to the conductors and insulated the soldering points, I wrapped the entire structure with FUM - from the thermistor to the rest of the insulation. One edge was treated with tsapon-varnish, and a terminal block was attached to the second:
Having inserted the resulting temperature sensor into the tube, I fixed it at the outlet with electrical tape:
The temperature sensor was connected to the circuit with a shielded wire to eliminate possible interference. Do not forget to also close the contacts that were connected to the old sensor, otherwise the heater circuit will remain open
Assembled view:
Perhaps not entirely aesthetically pleasing, but quite functional. Two months of operation have shown that the circuit operates in normal mode, no trigger effect is observed, and the accuracy of operation is noticeably higher than that of its mechanical counterpart.
When implementing the scheme, I was guided by the principle of “minimal intervention” - i.e. if necessary, everything can be quickly returned to normal. But I don't think I will need it.
Maxim Taranets, Kartaly 2016
2016-12-14 Evgeniy Fomenko
Method for repairing a thermostat
The first stage of repair is to disconnect the water heater from the electrical network, then drain the water, and remove the heating element from the water heater. Remove the thermostat from the heating element by carefully pulling it out. Drill out the copper rivets holding the body together, disconnect the body from the rod, this must be done carefully so as not to damage anything.
There are two methods for cleaning bimetallic plates: if the contamination (oxidation) is not very strong, try cleaning it with a cloth soaked in alcohol, inserting a piece between the plates and wiping; if such cleaning does not produce results, clean the plates with the finest grit sandpaper. It’s even better if it’s already used, so as not to break contacts.
The breaker contact (rocker) may have stuck to the housing. To fix this problem, disconnect the contacts and clean the area. The break contact should return to the upper position automatically.
If this does not happen, remove the “rocker” from the device, clean it with fine abrasive sandpaper, clean the place where it is installed (perhaps melted plastic has stuck there), and install it in its original place. If the “rocker” still does not return to its original place, glue a piece of insulating tape under it, selecting such a thickness so that the contact plate returns to the upper position.
Insert the rod back, tighten the housing using self-tapping screws, and insert it back into the heating element.
In addition to those described above, there are the following possible malfunctions thermostat, which can only be eliminated by replacing it:
- The copper tube has worn out.
- Electronics malfunction.
- Malfunction resulting from voltage drops.
If you find that your device has stopped working, there are ways to check the problem yourself. To check the operation of the thermostat for the water heater, you will need to remove the thermostat and set it in resistance change mode. We set the maximum possible temperature, measure the resistance in the input and output contacts of the device.
If the device shows infinite resistance, you can safely conclude that it is faulty. And if there is resistance, then turn the regulator to the highest small value and reconnect the contact tester. Next, using a lighter or candle, we heat the tube of the device; if the device is working properly, the relay will operate, which closes the circuit, and the resistance indicator will increase. If this does not happen, the device is faulty.
If you are unable to repair your thermostat, you should follow these recommendations to find a suitable device. The most the right decision will be purchasing the same device, from the same manufacturer.
However, if you haven’t found it, when choosing, pay attention to its dimensions, the method of attachment to the water heater, the number of functions performed (only temperature control, or also protective), and the voltage for which it is designed. When you go shopping for a new one, don't forget to take technical passport to a boiler or a faulty appliance.
Video about the thermostat design:
The storage electric water heater consists of the following elements:
- tank or housing;
- thermal insulation made of polyurethane;
- internal tank - a container in contact with water, covered with glass porcelain, enamel or stainless steel;
- magnesium anode that protects against corrosion;
- heating elements (heating elements);
- thermostat for temperature control;
- relief valve for relief overpressure in the tank.
The thermostat, like the heating element, are important components electric water heaters. The heating element heats the water, and the thermostat is responsible for maintaining, adjusting and heating the water to the required temperature. In addition, it is also responsible for the safety of the device, since it turns off the heating element when the water temperature becomes critical and steam begins to form.
Types of thermostats (thermostats) and operating principle
Typically, the following types of thermostats are used in water heaters:
- rod (bimetallic);
- capillary;
- electronic.
Operating principle capillary thermostat– pneumatic. The pressure inside the gas flask in which the thermostat is enclosed varies depending on the temperature. The change in pressure is transmitted to the electrical contacts through a pneumatic relay along the capillary.
An electronic safety and control thermostat is a more expensive thermostat for a water heater. The water temperature in the boiler is inversely proportional to the resistance electronic sensor. It is by this principle that the temperature of the water heater is controlled and adjusted.
Briefly, the operating principle of any thermostat can be formulated as follows:
- The required temperature level is set (lever, button, switch).
- The thermostat measures the water temperature and turns on the heating (heating element) if necessary.
- After desired value temperature is reached, the thermostat breaks the circuit and turns off the heating element.
- As soon as the water cools down, the thermostat for the water heater is activated again, the circuit is closed and the water is heated.
Submersible heating element - heating element
Such elements are a thin tube of copper or steel with a high-resistance metal wire and magnesium oxide inside for electrical insulation. It is mounted in the same flange where the thermostat for the water heater and the anode (magnesium) are located. Submersible elements reliably protected from water ingress, and their operating temperature reaches 300-400 degrees. Heating elements are distinguished by shape, power, size. The elements are connected to one or three phases.
Advantages of submersible elements:
- optimal combination of price and quality;
- high efficiency and reliability.
The design of the element is similar to the submersible type, with the only difference being that the body of such a heating element is made of refractory ceramic tubes. Mounted ceramic heating elements in an enamel housing with a thermostat and anode.
The advantages of such elements:
- quick and convenient replacement of elements in case of breakdown, which does not require draining the water;
- the enamel coating of the body completely protects against corrosion;
- resistance to scale formation, since the large area of the elements prevents them from overheating.
One of the most important parts for a water heater is the thermostat. It is the thermostat for the water heater that maintains a constant water temperature, protects against overheating, and, if necessary, performs operations to turn the water heater off and on. It is the thermostat that makes it possible to set temperatures and maintain automatic modes.
Basic principles of thermostat operation
Every water heater thermostat works on the same principle, regardless of the manufacturer. The thermostat is equipped screw design, at which the temperature required by the user is set. After tightening the shut-off valve, cold and hot water begins to flow into the water heater, after which the adjustment processes begin to work.
To obtain the desired temperature in the water heater, hot water has the advantage. It flows until it reaches the specified parameters, only under this condition does mixing with cold begin. Depending on the type of water heater - instantaneous or storage, the power of the heating element is selected. Most often, it is in flow heaters it has great power.
How to choose the right thermostat
When choosing a heater or additional thermostat installation, you should remember that heating tank and the thermostat itself has different warranty conditions. This is due to the fact that many skillful water heater owners, when different types in case of breakdowns they take care of do-it-yourself repair. The most common thermostat breakdowns:
- copper capillary tube very sensitive to mechanical damage; once it fails, it cannot be repaired, it should only be replaced with a new one;
- poor adhesion of the electrical connectors of the thermostat and heating element;
- insufficient quantity hot water regarding the total power of the water heater may be due to incorrect heating element adjustment;
- too hot water indicates a failure of the thermostat control structure;
- if scale has formed and its amount exceeds the permissible limit, the thermostat will turn on and off very often;
- failure of the electrical components of the water heater is most often caused by constant voltage drops in the network; to ensure operational safety, the source must be identified uninterruptible power supply or voltage stabilizer.
If you need to replace a thermostat for a water heater, you need to know what types exist:
- Rod thermostat– consists of a steel rod, which is designed to be placed in the heating element tube. Depending on the power and volume of the water heater, the length of the thermostat rod is determined. It ranges from 25 to 45 centimeters.
- Thermostat, which consists of a polyester housing. It has a built-in switching device (thermal regulator). Such a device is called capillary. The principle of its operation is based on the volume of expansion fluid in the capillary tube. The expansion fluid acts on the membrane installed in the thermostat and switches the electrical contact.
- There are two types of electronic thermostats: control thermostat and safety thermostat. Their operation is the same as that of fuses, which have a certain resistance.
The thermostat for a water heater is precisely the part that is the basis for the entire functioning of the boiler. With correctly selected technical specifications and all operating conditions are met, the water heater will last for a long time no cleaning or damage.
The thermostat for your water heater plays as important a role as the fuse in any electrical circuit. The user sets the required water temperature in the water heater, and the thermostat maintains it. That is, it allows the heating element to work until the water temperature reaches a set value.
This is what the device looks like for adjusting the temperature of water heating and for emergency shutdown
Then the heating element stops working. The water temperature decreases (forced or naturally) and the thermostat again gives a signal to the heating element to begin its direct duties.
Separate, specially designed types of thermostats have additional function– turn off the power supply to the heating element if the latter breaks down. This avoids the possibility of electrical shock, which often happens with ungrounded boilers.
Types of thermostats
Today, many types of thermostats have been developed, but if we talk about devices specifically for boilers, the three most successful are:
- Rod. Such a thermostat is represented by a tube of small diameter (usually up to 10 mm) and short length (no more than 35 cm). The operating principle is based on the elementary laws of physics: when heated, the tube expands linearly, which allows you to press the switch. Such thermostats have long been the most common in boilers. However, their accuracy left much to be desired when hot water left the water heater. incoming cold water instantly cooled the thermostat due to the latter’s close location to the inlet cold water. Thus, the boiler could work beyond the allotted time, and this significantly affected financial costs.
- Capillary. A more progressive type of thermostat, also working according to the laws of physics. The tube in which the temperature-sensitive cylinder with liquid is located is usually made of a material that cannot be oxidized over a long period of time. Inside the cylinder there is a liquid that has a different density from water. When heated, the density of the liquid changes, the volume changes accordingly, and the liquid presses on a special membrane, which turns off the power. Such thermostats are more accurate when compared with rod thermostats. The temperature deviation is approximately 3°C.
- Electronic. A more modern type and, accordingly, more accurate. It usually works in tandem with a protective relay - if the boiler is empty when voltage is supplied to the heating element, then the protection will work and turn off the power.
According to another classification, all thermostats can be divided into:
- Electromechanical and electronic. The first type works due to bimetallic elements, the second - thanks to electronic special sensors.
- Simple and programmable. In the first type, the temperature is set manually mechanically. The second type is more precise in its work.
- Overhead and mortise. For boilers, the overhead type is most often used if the control is electronic, and the mortise type if the control is mechanical.
Another interesting option– thermostats designed for indirect heating boilers. Such boilers allow you to heat water using only power for heating device, which means it is obvious significant savings. But circulating in heating system the liquid cannot heat above a given level, while for a boiler the consumer may need a different temperature (and most often this happens). In this case, you should buy a thermostat specially designed for this purpose.
Having carefully studied the articles on self-production, you can try to make a thermostat yourself.
Malfunctions and their solutions
The thermostat for your water heater may fail. Unfortunately, such phenomena are not uncommon, but there is nothing fatal here. Firstly, as a rule, there is no repair - a thermostat that has worked faithfully is thrown away and a new one is bought. Buy the same or with a different resistance - the choice is up to the consumer. Secondly, when correct operation water heater thermostat breakdown can be avoided or, in extreme cases, its life can be significantly extended.
How does a consumer notice a broken thermostat? As a rule, this is the most common method - the water is not heated in the boiler. In this case, there may be either a malfunction of the heating element, or a malfunction of the thermostat itself, or (less commonly) a malfunction of both elements. To check the latter, its resistance should be measured.
If during testing the picture on the display of the test device does not change, you need to buy a new thermostat. It's not that much money, so there's no need to grieve. Another option for testing the thermostat is possible: measuring the resistance when the thermostat itself heats up. If even then the test device does not show any changes, that’s it, now it’s time to go to the store.
How to choose
Typically, a faulty thermostat can be replaced with a similar one in shape and operating principle. However, if it is possible to buy and install another thermostat and there is an urgent need for it, then why not. The main thing is to be able to choose the right device and install it correctly. Although here, too, the consumer can be helped by the Internet or a consultant at the point of sale.
But we should not forget: any independent actions without certain knowledge and strict adherence to safety rules can lead to a very unpleasant outcome.
It would seem that the heating element or volume should be important in a boiler, but, as it turned out, the thermostat and its role cannot be neglected. By setting the desired temperature and protecting the boiler from overheating, the thermostat is extremely important in the operation of the heating device.
Purpose of a thermostat for a water heater
The thermostat for a water heater is one of the elements of any boiler. If it were not for its presence in the design of the water heater, then calling such a device automatic would be a great exaggeration.
