Vaillant EcoTec Plus Stove - Error F76 Displayed, Water Heating Issue: Causes & Fixes

I have a problem with the Vaillant EcoTec plus stove, because when the water is heating up, the error F76 appears on the display - the water is not heated as usual.
Has anyone had a similar problem? What is the cause and what will need to be fixed?

At the beginning, you did not specify the exact model of the Vaillant ecoTEC plus boiler.

Generally, older models of ecoTEC plus boilers have a built-in temperature sensor (thermistor?) In the main heat exchanger casing - top left. As the trainers in Vaillant say, when this sensor works and displays error F76, the entire main heat exchanger needs to be replaced, and it costs several thousand. PLN.
This sensor / fuse is permanently installed and once it has tripped it cannot be replaced. The reason for its activation was very high temperature. You need to check what caused the overheating - dirty exchanger in the combustion chamber or stony on the water side, or a system with high air in it and it did not pick up heat. The heat exchanger may become unsealed and water with CO may get into the combustion chamber and further into the sewage system through the condensate drain.

Apparently, someone once "cheated" this sensor, but I don't even know how.

It is an error related to the safety system which warns against overheating of the boiler. Mainly, this system is responsible for the lack of heat reception from the boiler, so there may be several reasons - you have to check and eliminate it one by one.

In short - there is such a STB overheating sensor on the heat exchanger - if the temperature in the exchanger is too high, it short-circuits and the F76 error is displayed. But it is known, it is electronics and it happens that the sensor is fine, but the cables are defective, contacts, clogged filters, closed valves, air in the exchanger, etc.

In your case - if you are lucky, you will have a short circuit "on your way" to the sensor. Unlucky - the main exchanger needs to be replaced.
I don't know what series of boiler you have (year of production), but these sensors are mostly non-replaceable, integrated with the exchanger. They are replaced together with the exchanger.

It is a safety system that is to function in such a way as to prevent accidents, so any interference by inexperienced people can end in a tragedy.

I have an appointment with a company that deals with the repair of this type of stoves, we'll see what he says.

Painkiller1 - and how was the problem solved? Now I have a similar problem and I am wondering whether to combine or replace the entire exchanger module.

What is your exact boiler model? There is a sticker under the boiler and there is the boiler type:
VC (or VCW) xxx / yz.

I'll check when I get home. This is the 18k ecoTec plus VC with hopper. 10 years.

So probably VC 186 / 3-5.
But check it out.

That's right, it's VC 186 / 3-5.
The story is like this. Every other day he reports error F.76 to me, every time when he is working in DHW mode. I measured the sensor in the TSD 1902 exchanger body and it comes out close to zero resistance. It doesn't look weird or burnt.
To survive these cold days, I reduced the power supply parameters for the DHW mode to 60 ° C. It is better, i.e. in the morning it even heated the water.

Well, now the question is whether to look for a new TSD1902, or, as Vaillant recommends, replacement of the exchanger module, or maybe some other way with a sensor replacement?

Vaillant recommends replacing the exchanger, assuming it has broken Generally, these TSD sensors are not fault-free. It is best if you ask a service technician to check the exhaust gas temperature and determine if it is normal. Most service technicians have such sensors when dismantling damaged exchangers. I would like to add that in new boilers, this sensor is no longer present and it also works.

And do you know what is the nominal resistance of this sensor? On the manufacturer's website there are resistance characteristics as a function of temperature, but the model codes do not match the OEMs. The service technician was and said that this sensor causes an error, the exchanger is ok, now I am waiting for the second visit with the sensor to be replaced + inspection. Only this sensor can not get and I do not know how long it will take. That's why I have the following options: insert a resistor in the connector and reduce the DHW supply parameters or block the DHW at all and quickly put a reserve current stage in the system.

As for Vaillant. I called their hotline with a simple question, let them give me a little info on the characteristics of this OEM. You said - clearly - that you would not share such information even with a longtime customer (I have 2 Vaillant boilers). As for the problem, the entire exchanger needs to be replaced. To my question whether it happens that this sensor fails despite an efficient exchanger, he did not answer. When asked what the new model differs from the old boiler, the one with a sensor, he said that the new one had slightly different security features, so they did not provide a sensor on the exchanger chamber. When asked if this remodeling was caused by problems with this sensor and the assumption that it would not be on the spare parts list, you said no, because the new boiler has different safeguards. When asked how these new-different security features differ from those in the old boiler, you did not answer me. So welcome to the world of modular responses.

Hello
Has the problem been resolved? What is the characteristics of TSD 1902, what is the OEM code and what can you replace it with?

I found the datasheet for the Tasseron TSD series:
[url=] http://www.tasseron.nl/sites/default/files/product_groups/downloads/Tasseron_TSD_2.pdf [/url]

Nobody will provide information on the characteristics of the OEM. The problem was solved because the service technician somehow acquired such an element. The exchange confirmed that, however, these elements deteriorate. Nominal resistance close to 0.

I think that the best summary of this failure is the text heard in the Vaillant headquarters: "what people exchange such crap, let them replace the entire module and there will be cash".

Note that these sensors are usually mounted in plastic heat exchangers on the outside. All acid iron ones have less risk of damage. Often, after a few years, silt and other sediments, for example from steel radiators, can clog the secondary exchanger and then the sensor fails. In Vaillant there are 3 coils in the exchanger and after clogging, the water flows correctly for example through 2 and the third overheats. Once upon a time, the exhaust gas temperature when heating domestic hot water was normal, and you could clearly smell the burning. Not to mention a third-party exchanger without a sensor, where the customer neglected the service and the exit from the exchanger to the chimney melted. Therefore, replacing the sensor does not necessarily have any effect and may even endanger the user.

smq80 wrote:

Nobody will provide information on the characteristics of the OEM. The problem was solved because the service technician somehow acquired such an element. The exchange confirmed that, however, these elements deteriorate. Nominal resistance close to 0.

Buddy, I have the same problem with Vaillant VC plus. You mean that the new sensor is supposed to have about 0 Ohm, and if it overheats, it is a break forever / burned out, or the one you had before had 0 ? and was damaged?

New close to 0 ?.

Check how you make money:
https://allegrolokalnie.pl/oferta/tasseron-tsd-1902-czujnik-temperatury-vaillant
250 + 20 PLN, used !!!
A broken one can sometimes be skillfully regenerated with a capacitor, so safety will not suffer.

Hello
I have an Ecotec plus vc pl 186 / 3-5 boiler and error F.76 appears every few domestic hot water heating. Sometimes it is enough to reset the burner and a few more heatings are fine, and sometimes you have to turn the boiler off for several minutes and turn it on. I measured the resistance of the overheating sensor right after the error and it was 7 k? and it decreased as the temperature decreased. I noticed that by moving the plug it shows an error, so I cleaned the contacts, bent the pins in the plug, but it did not help. It looks as if there was a break inside the sensor which was revealed under the influence of temperature.
Has anyone found a solution? Where to buy a new sensor?

This overheat sensor is Tessaron tsd1902 and if it's 0 Ohm then everything is fine. The problem comes when he's on a break. From what the service technician said, it happened that the sensors themselves collapsed and in the absence of spare parts you can temporarily bridge it, but this is at your own risk. You can also get them from disassembly. Did you solve your problem?

Painkiller1 wrote:

Has anyone had a similar problem? What is the cause and what will need to be fixed?

The reasons are, as he described:

ls_77 wrote:

The reason for its operation was very high temperature. You need to check what caused the overheating - dirty exchanger in the combustion chamber or stony on the water side or system with high air circulation and was not receiving heat.

It is often damaged by the user himself, namely the air in the exchanger after draining the water, e.g. when checking the pressure of the diaphragm vessel and sudden, incompetent filling of the installation, and then quick boiler start - the fuse overheats.
(see # 2: https://www.elektroda.pl/rtvforum/topic3770267.html#19201475)

Basically not a sensor, but a thermal fuse, so if it is good it should be NC, the resistance should be close to zero "0" ?.
Otherwise this thermal fuse inside irreversibly becomes NO, or its resistance is much higher than "0" ?, and the furnace electronics see it as damage to the exchanger.
For the main plastic exchanger, I do not recommend bridging this fuse for safety reasons!
Therefore, it is not commercially available as a separate new part (although it is removable), but when purchased it is a complete set with an exchanger, nearly 2,000 PLN.

This sensor can behave quite strange. After the stove is turned off, everything works again, but sometimes it comes back after a few days, sometimes after a few hours, and sometimes you have to wait longer. It temporarily changes state to NO, so this suggests its failure if the system is full, vented and there is pressure. In my opinion, it is not that these sensors are failure-free.

By the way, I have a question? Has anyone mentioned it? You would have to drain the water for this, or does he only measure the temperature of the exhaust gases?

raceman wrote:

You would have to drain the water for this, or does he only measure the temperature of the exhaust gases?

In principle, it is not necessary to drain the water for the test.
It doesn't measure the exhaust gas temperature, but it is a STB. (limit exceeding the maximum permissible temperature, e.g. 95 ° C)

raceman wrote:

Temporarily changes to NO

If it is temporary, it means poor contact of connectors, solder contact, broken wires and the connectors themselves all the way to the motherboard.

I'm not talking about the test because I know how to check it.
I'm more interested in what needs to be done to REPLACE it. So do you need to drain the water? Is he sealed with something? Is it screwed in or on a latch?
My question is - what does the sensor measure? Exhaust gas temperature or water temperature or what?

raceman wrote:

I am more interested in what needs to be done to REPLACE it. So do you need to drain the water? Is he sealed with something? Is it screwed in or on a latch?

In brief:
- turn off the boiler, preferably from the socket 230V AC,
- drain the water from the central heating circuit
- disconnect the wires from the fuse connector,
- gently turn it 1/2 turn counterclockwise (with some resistance because it has a sealing O-ring) and remove it upwards.
- assembly in reverse order with venting, also with description (see # 2: https://www.elektroda.pl/rtvforum/topic3770267.html#19201475)

raceman wrote:

My question is - what does the sensor measure? Exhaust gas temperature or water temperature or what?

Exceeding the emergency threshold of the boiler! Overheating of the STB, basically it is water, and in the event of a lack of water, then the flue gas, and here the boiler is irreversibly turned off until it is repaired or replaced.

raceman wrote:

This sensor can behave quite strange. After turning off the stove, everything works again, but sometimes it comes back after a few days, sometimes after a few hours and sometimes you have to wait longer. It temporarily changes state to NO, so this suggests its failure if the system is full, vented and there is pressure. In my opinion, it is not that these sensors are failure-free.

By the way, I have a question? Has anyone ever mentioned it? You would have to drain the water for this, or does he only measure the temperature of the exhaust gases?

For me, the sensor also behaved like that, it could overheat several times a day to work properly for a few days. I exchanged it for a used one, and after trouble.
You do not need to drain the water for replacement, there is a gasket on the sensor, but there is no water under it, you turn it 90 degrees and pull it out.

Thanks. Now I do not know if it is necessary or not to drain the water? I understand that you did it yourself and did not flush so?

That's right, I replaced the sensor myself. The sensor is not in contact with water. I also tested the plug bridging, everything works just fear that there is no overheating protection. There are many offers of parts for this boiler on oeliks, including used sensors and entire exchangers with sensors.

Thanks, then I will try to replace as soon as the frost subsides. I have already bought the sensor, used, but functional.
I have exactly the same feeling that it will be better and safer if there is some security than the jumper itself

raceman wrote:

In my opinion, it is not that these sensors are failure-free.

raceman wrote:

I have exactly the same feeling that it will be better and safer if there is some security than the jumper itself

TomekM77 wrote:

I also tested the plug bridging, everything works just fear that there is no overheating protection.

No jumper!

ROWE wrote:

It doesn't measure the exhaust gas temperature, but it is a STB. (limit exceeding the maximum permissible temperature, e.g. 95 ° C)

And exactly, if the F 76 error is displayed, then TSD 1902, it can be even close to its max. permissible temperature 167 ° C.
Therefore, in most cases, the cause lies outside of the TSD 1902, and the STB is the ultimate security guard.
Exceeding the temperature limit damages the TSD 1902 irretrievably!

1) You said you need to drain the water, which is not true!
2) In our case, the sensor did not break permanently, but behaved unpredictably.
3) I asked what this sensor measures, you just repeat the mantra STR, STB.
Have you ever seen this cauldron with your eyes and undressed?