Are you familiar with the situation that you have to repair an expensive part, and the budget for this repair is growing? Surely you know what costs can and should be considered unnecessary. For example, you have a gas boiler and you don’t want to spend up to 30 percent of the cost of the entire device for repairing a single part. If you do not know how to weld a gas boiler heat exchanger, just read our article and you will learn how to do it.
Thanks to this article, you will learn the procedure for repairing a heat exchanger - parts that often cause boilers to break. We talked about soldering heat exchangers in different ways. Using our recommendations, you can independently repair a failed part.
In domestic conditions, heat exchangers are repaired by soldering. Welding is literally used in manufacturing, sometimes with the help of robotic devices. Leave a heat exchanger with extensive structural damage to the craftsmen, but in the case of small holes in the part, soldering can help. Learn more about this.
The content of the article:
- Removing the heat exchanger from the boiler
-
Gas boiler heat exchanger brazing
- Preparation of materials before soldering
- How to solder the boiler heat exchanger?
- Cold welding as a repair option
- Conclusions and useful video on the topic
Removing the heat exchanger from the boiler
Gas boilers are equipped with heat exchangers, sometimes they are called boiler radiators, in which some sources transfer thermal energy to others. Most boilers have primary and secondary heat exchangers, while others have combined or bithermal heat exchangers.
All types of exchangers are affected by unfavorable factors. The quality of the metal deteriorates, the permeability of the channels decreases, the water pressure hits the walls. The primary and bithermal are affected by the flame of the main burner.
In bithermic heat exchangers, the water supply channel is located inside the heating line - if it were the other way around, the heat exchangers would more often fail
Worn-out exchangers may have holes. Given the cost of this part, it makes sense to repair them rather than replace them immediately. Moreover, it is not always possible to find an analogue.
If the heat exchanger is leaking in a gas boiler, you will notice leaks next to household appliances or an error on the display. Remove the problematic part if necessary.
First, do this:
- Disconnect the boiler from electricity and gas.
- Shut off the flow of heating medium into and out of the heating system. Turn on the tap to supply tap water to the boiler.
- Drain the remaining water in the device.
- Remove the boiler lid.
- Bleed air through the vent.
- Check the inside of the appliance. See if there is moisture somewhere and wipe it off.
To access the primary or bithermal heat exchanger, free the combustion chamber from the elements that fit it. Remove the pipe that supplies gas to the burner. Disconnect the electrical wires from the combustion chamber. If you forget this nuance, then due to carelessness you can damage them.
Disconnect the sensors, pipes of the heating circuit, remove the pipes of both circuits from the bithermal exchanger. Remove the components that prevent the device from being pulled out of the boiler.
Disconnect and pull out the combustion chamber. Remove the top and front covers. Remove the hardware under the heat exchanger and pull it out.
Due to water leakage from the heat exchanger, deposits form and the condition of the boiler elements deteriorates, sensors may fail, after which the furnace will not start
To get the secondary heat exchanger, remove the board and other electronic elements, unscrew and remove anything that would prevent the unit from being pulled out of the boiler. Isolate the contents of the device from the ingress of water from the exchanger and from the channels that fit to it.
But a malfunction of the heat exchanger is not the only reason why the boiler can leak. We described in detail about other possible causes of leaks and ways to eliminate them in this article.
Gas boiler heat exchanger brazing
All water, air and solids are removed from the exchanger. Blow through the hose by machine, and blow out the remains by mouth.
For soldering, four components are used:
- soldering tool (gas torch, blowtorch or soldering iron);
- solder;
- flux;
- before and after stripping tools.
Solder is a material for joining workpieces that has a lower melting point than the base being processed. Solders are usually made from metals. They are produced in the form of wire, embedded parts, pastes, foil, powders, rods and granules. Wires are most suitable for brazing the heat exchanger. Take this one.
To repair the heat exchanger, a high-temperature solder with a lower melting point, but not lower than 700 ° C, from the same material and with similar physical and mechanical properties, is chosen. The anti-corrosion properties and the specific conductivity of the wire are also taken into account.
Copper, stainless steel and cast iron are common raw materials for exchangers, and zinc is often added to the base. For brazing copper heat exchangers, they are more often used copper-zinc solders with inclusions that neutralize the dangerous effects of vapors.
The solder in the rods is not as convenient as the wire solder, but it can also be bent by hand, even with a large diameter, and the resulting solder will be quite tough
Solid high-temperature solders are marked PSr, PMTs, PMT, etc.
Copper-zinc denote PMC and are numbered based on the melting point:
- PMTs-36 - from 825 ° C;
- PMTs-42 - from 833 ° C;
- PMTs-54 - from 860 ° C.
Anyone can solder a standard heat exchanger of a gas boiler, but whether this can be done depends on the materials of the part.
Good solders give tight seams. The components of such alloys penetrate into the brazed surface by diffusion, and the base dissolves in a small amount in the auxiliary material. After solidification, a homogeneous layer appears.
Flux is a substance for removing oxides from the brazed base, increasing the fluidity of the solder, reducing the surface tension, and better wetting the workpiece. Heat exchangers are combined with universal and special products. Solder pastes usually contain copper, which is good for the heat exchanger. Mixtures with silver are fine too.
Preparation of materials before soldering
The soldering iron tip is tinned. The instrument is heated until the tip is slightly reddened and covered with a thin layer of solder, while the oxidation film is removed. The tip and wire are dipped into the flux. At the tinning stage, rosin or resin can be used for this.
After the smoke is released, the sting is held for a few more seconds. Then the soldering iron with solder is dipped into the flux three to four times.
The devices are tinned after purchase, and then from time to time - with frequent use. The tip of another soldering iron is sometimes used as a basis for tinning.
The photo shows tinning - after that it does not hurt to press the sting against a wooden board with resin, which will also even out the solder layer
If the condition of the solder is not the best, then it should be cleaned of dirt and oxides. Preheat the end of the solder wire to operating temperature and immerse it in the flux, press firmly against the hard surface on which it is located.
If there is no new wire, then the old one can be treated with a base cleaner, such as:
- abrasive;
- solder paste;
- acid for tinning.
Before soldering, dust is removed from the surface of the heat exchanger so that sparks do not appear during operation. The place with the fistula is treated with a cleaning sponge or fine-grained sandpaper, wiped with a solvent to remove all chemical compounds.
Then the problem area is heated with a hair dryer for better performance and to evaporate any remaining moisture. Otherwise, it will come out abruptly during operation and displace the solder. After warming up, the area is cleaned again.
How to solder the boiler heat exchanger?
A small fistula on the heat exchanger is found by green spots, but if such a shade is present on most of the device, then the condition of the coating, the evenness of the color, are taken into account.
The soldering agent is chosen according to the situation. A soldering iron is suitable for fine work. A large tongue of flame from a gas burner will warm up the problem area well, but the power of the device may not be enough, contrary to expectations. A soldering iron also needs to be selected powerful.
Choose the correct nozzle for the burner - the flame should be about 2 cm wide, and rotated for convenience, and when working, keep it so that the fire is evenly distributed over the surface
Most of the work looks simple. A flux is placed on a heated place, after which they begin to solder. The solder is placed on the heat exchanger with its tip, the soldering iron is attached to it and gradually heated. The wire will begin to interact with the flux and base. The remaining uneven mass after soldering is distributed.
In case of gas burner, take the usual standalone or something more productive. For example, powered by a large balloon. Never turn on the maximum flame. Apply the solder after the color of the flux becomes brighter, such as silver instead of gray.
Keep the torch at a distance so that the wire will melt more from the heated heat exchanger rather than the fire. For a small fistula, a half-minute soldering may be enough. Detailed instructions on soldering can be found in this material.
Do not overheat the base and solder during soldering - the latter will be poorly fixed. Make sure that the resulting structure is not loose, and the color is not expressed matte. Soldering ideally restores the entire problem area, and if this is not the case, then another approach will be needed.
Bring the temperature of the soldering iron to 20 degrees above the melting point of the solder. To clean the finished joint, use braids and spring removers - the tools will also remove the remaining flux. Wipe off the exchanger with a damp cloth and remove all microparticles.
For normal operation of the boiler combustion chamber, the soldering point must be cleaned, and some disturbance of the shape for the primary heat exchangers does not matter
Water will not be allowed to pass through the repaired heat exchanger for another 5-10 minutes. In any case, let the part cool completely. Run only clean water on the first day after renovation. Make sure there is no rust.
Bleed the air from the system again and carry out a test run of the boiler. Check full load operation. Run cold and hot water through the exchanger. After several temperature cycles, the exchanger may be leaking again.
The repaired part must be able to withstand thermal deformations. As a safety net, coat the joint on the exchanger with heat-resistant paint to increase durability. Repeat the heat exchanger test on the following days.
We also recommend reading about other malfunctions of the heat exchangers of gas boilers. More details - go to link.
Cold welding as a repair option
The so-called cold welding is made on the basis of adhesives. The popular raw material is epoxy resin. Do not confuse material and cold welding in understanding the technological process with plastic deformation of metals without heating.
Choose the most moisture resistant raw material available on the market. When starting out, wear gloves and soften the weld with your fingers. Do this until the mass becomes plastic. Place the material on the fistula and spread over as large an area as possible. Make the layer thick, but not necessarily the bulkier the better. Apply with a wooden stick.
Cold welding is used on copper, brass, bronze, cast iron, iron, alloys, and also on ceramics, wood, stone, but the final quality of the joint largely depends on the work itself
Wait for the finished layer to harden and surface sand the area with fine-grained sandpaper and a damp cloth.
Wait half an hour at first for better hardening. The recommended 3-5 minutes are sometimes not enough. Check the quality of the joint with temperature contrast and water pressure.
Conclusions and useful video on the topic
An alternative way to extend the operation of the primary boiler heat exchanger:
Soldering the heat exchanger roll with two gas burners:
There are three easy ways to seal a hole in a heat exchanger: flame, sting, and adhesive. Most often, we are talking about a narrow hole in the primary or bithermal exchanger, so the listed methods are quite enough.
Leave complex damage to the masters. But, in which case, you will find something to solder the heat exchanger, get it out of the gas boiler and choose the solder yourself. If possible, act independently and remember the importance of preparatory work.
Write comments, ask questions on the topic of the article. If you have a boiler, tell us if something happened to its heat exchanger. Write about your experience in soldering and repairing exchangers or other boiler parts. The feedback form is located under the article.
