Possible solutions for an boiler starts and stops


Has it ever happened to you that your boiler does not start when you open the tap? Or that it constantly turns off and on? Or is there a red light on the control panel? When a diesel boiler starts and stops, this can be a symptom of several things. And we know that this is not pleasant, because it can leave you without heating when you need it most, in addition to the fact that the fuel cost is higher. Therefore, follow us in this article, as we will be looking at the causes and possible solutions for when a diesel boiler starts and stops on its own.


When is it normal for the burner to turn on and off?

The burner in the oil boiler turns on and off, sometimes it is part of its normal operation. This is due to the equipment’s power regulation and modulation system, or because the equipment has already reached the temperature that you indicated with the thermostat, and then it turns off until it is necessary to change the ambient temperature again.

Another case in which it is normal for the boiler to turn off automatically occurs when you have programmed the thermostat for a much higher temperature than the ambient temperature (more than 10 degrees difference, for example), and then the house takes more than one cycle switching off and on from the boiler before reaching the indicated temperature. In these cases, the boiler can be turned off and on even before reaching a comfortable temperature.

Keep in mind that the water in the boiler heats up much faster than the domestic environment, and when the boiler has already heated the water, its work has been done for the time being and it is normal for it to turn off, especially if it is a hot water accumulator. The only thing left is for the hot water to warm up the temperature of the hearth, but at times this does not correspond to the boiler itself, and it is normal for the burner to turn off momentarily and then turn on again.


Especially if your boiler is a modulating boiler (a high-tech heating system that is very different from the usual On/Off system), switching on and off frequently is part of its ultra-efficient normal operation, seeking to precisely provide exactly a comfortable temperature with the minimum consumption of fuel, precisely based on the continuous turning off and on of the burner.

In any of these cases, if the boiler turns off and on, don’t worry, because it is working exactly as intended by the manufacturer. However, this is not always the case. It is important to learn to distinguish when the automatic shutdown is due to the normal operation of the boiler, and when it is due to true faults or breakdowns. Keep in mind that a boiler that turns on and off continuously uses more fuel unnecessarily and in the long run reduces its useful life due to wear and tear.


Causes and solutions for a diesel oil boiler that stops

As we have already seen, the fact that a boiler turns off by itself before having generated the desired temperature is not necessarily something abnormal. But it can be. Sometimes they are true symptoms of a problem, which can be due to many causes, and therefore can have different solutions. Let’s go from the simple to the complex.

The boiler lacks general maintenance

The law establishes that the boilers must receive general maintenance at least once a year, for reasons of safety, fuel economy, and reduction of emitting polluting emissions into the atmosphere. Many routine boiler problems (including excessively high fuel bills) are sometimes magically resolved with good general maintenance.


Maybe your boiler is just lacking in general maintenance, and since that creates a number of problems, any one of them could be causing the boiler to turn on and off on its own. For example, if the electrodes are dirty or misaligned, if the heating recirculation pump is blocked, or if there is a routine blockage or cut in the fuel supply: all these can cause unnecessary switching on and off.

If in your case you haven’t done maintenance for a long time, the mysterious automatic switching on and off of your boiler may not be due to anything serious. See to it that your boiler receives its maintenance, and maybe that will solve everything.

There may be failures of different types in the electrical supply

Faults in the electricity supply can cause the boiler to turn off and on by itself. It seems too simple, but it can happen, and you should rule out this cause before thinking about more complex ones.

It is not impossible that the power socket where you connect your boiler could have a false contact, short circuit, be stripped, have a cut or pinched cable, or any other similar type of fault. Moisture is a bad companion in these cases because it creates bridges between cables that must be kept isolated.


This will obviously cause problems with the automatic switching on and off of the boiler. Check the power sockets and electrical current paths, and if you notice something strange, contact an electrician to resolve this situation, which is actually unrelated to the boiler itself but can cause problems even in the rest of the electrical installation of your home.

The thermostat is damaged, faulty or incorrectly installed

Logically, the abnormal automatic switching on and off of the boiler may be due to the fact that the thermostat has problems telling the boiler when it can be switched off and when it should be switched on because the temperature has dropped. That is exactly its function, and it may be doing it wrong.

You must rule out that it is the thermostat, before trying to detect problems that are really due to the boiler. It may be faulty, broken, or simply poorly installed. In the latter case, you can take care of this by hiring a technician so that the thermostat is properly installed.


And on some occasions, the problem can also be at the origin (the boiler) and not at the terminal (the thermostat). In other words, it may be that the temperature probe has broken down, which is responsible for detecting whether the water is hot or not (and for sending the order to heat more water to the boiler). Power offs and one can become erratic.

Problem connecting the photocell to the control unit

Whenever there are symptoms such as the boiler turning on and off unnecessarily (especially if it does so at regular intervals), it is necessary to check if there is a connection problem between the photocell and the control unit (the programmer). If the photocell is faulty, dirty, misaligned, or poorly connected, the boiler can work like this, with random switching on and off.

If it is faulty, you should call a technician to replace it. If it is poorly connected or misaligned, it must be placed correctly, which may also have to be a technician’s job. If it’s dirty, you can clean it with a dry cloth or kitchen paper, perhaps using ammonia. Consult your manufacturer’s manual. Some photocells tend to get dirty faster than others due to misalignment with the burner.

The boiler does not start because there is not enough pressure

This is probably the simplest cause of all, and it may be resolved by supplying the necessary pressure to the boiler through the usual means. It’s that simple. As with problems of excess pressure in boilers, there can be several causes of faults due to low pressure:

  • Little water flow (due to a bad water installation, supply failures, calcification, etc.)
  • Some valve has closed inadvertently. It seems silly, but it can happen. Check the valves to see if any were locked.
  • Something that prevents the pump from circulating the water properly. The pump itself may be faulty, dirty, or suffer from a lack of maintenance.
  • An insufficient number of radiators, that is: the power generated by the boiler is greater than that required in the home, and for this reason, the burner goes out.
  • Need to bleed the radiators. Radiators must be purged at least once a year. Start with the radiator closest to the boiler. Place a container so that the water does not fall on the floor, turn the valve (with your hand or a screwdriver), and let the waterfall until the jet is completely fluid, a sign that it no longer has air. Close the water valve and repeat the same technique with each radiator.

Check if you have any of these problems of insufficient pressure in the boiler, and solve them. In the event that the power generated by the boiler is greater than that needed by the home, it is best to adjust the power of the boiler to what is really needed at home, in order to prevent it from turning on and off, in addition to considerably reducing fuel consumption.

Obstruction of smoke evacuation

Every system that works by burning a substance generates residual fumes that need to be expelled from the system so that it can continue to function properly. In the case of boilers, this function is fulfilled by chimneys.


If for some reason the smoke evacuation does not work or becomes clogged, the system overloads or overheats, and it is normal for the manufacturer to have incorporated some automatic shutdown mechanism for these cases, with the aim of avoiding greater evils, such as explosions or more serious faults. That is, if the chimney does not expel the air well, the boiler can be turned off for safety.

Check to see if your boiler is expelling smoke well, or if the chimney is clogged or clogged by the same soot or something else. If so, the solution will be to call a professional chimney sweep, or even chimney sweep yourself. There are contemporary methods that facilitate this work, although you can always resort to traditional brooms for chimney sweeping.

Finally, it must be said that it is unlikely that the chimneys have any problem beyond dirt. Boilers are currently manufactured with a forced draft design, thanks to which the smoke outlet does not usually cause serious problems.

The boiler starts and turns off by itself: conclusions

Many people wonder why their boiler keeps turning on and off, even though the domestic heating and domestic water have the temperature programmed into the boiler. As we have explained in this article, this can sometimes be part of the normal operation of the boiler, and sometimes it can be a symptom of various faults.

In general, if the boiler turns on and off by itself due to a fault, it can mean that there is low water pressure, that there is a problem with the thermostat or with the lack of water flow due to a valve that was accidentally closed, or to that the pump does not circulate the water in the system properly, there may be problems with the expansion vessel or the photocell, or there may be obstructions in the pipes, which has a bad influence on the water flow, which does not reach the pressure that the boiler needs.

In any case, it is best that most of these problems are not solved by you, but by the qualified personnel of the company that manufactured your boiler. Boilers are complicated and exact pieces of equipment, with which care must be taken. You can request assistance on-site or online. The vast majority of boiler trading companies offer maintenance and repair services. Perhaps a normal, planned expense is more convenient than a large, unexpected expense in repairs due to lack of maintenance .

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