Minimax Termet Boiler: L3 Code, Overheating & Temperature Control Issues - Solutions & Fixes

Hello gentlemen.
I have a problem as in the topic - after setting the heating of the central heating boiler to, for example, a temperature of 60 degrees C, everything is OK. But after reaching the set point, the temperature continues to rise until the boiler is turned off, and then L3 on the display turns on. According to the service book, this is information about exceeding the temperature by 3 degrees from the set temperature, then only the pump works for about 3 minutes to cool down the exchanger - and I agree with it here. The boiler is 6 years old. Everything was OK so far. My actions to fix the fault:
All filters cleared
Descaled heater and plate exchanger (I personally unscrewed them) - with a special means - it was even boiling a little
All connections have been checked for tightness
Both NTC sensors cleaned (although they have little to do with it)
Entire boiler purged with air.
The entire installation, including the boiler, is sure to be deaerated.
Last year, I replaced the water pressure sensor
I know for sure- that this type is definitely not the case
All arguments about him are over.
Please help. It's getting colder

After reaching the set temperature, the boiler continues to heat - write specifically how much it heats up and at what temperature L3 turns on. L3 is the normal operation of the boiler. If the boiler actually overheats the water, the NTC sensor needs to be replaced, "although it has little to do with it," you say.

So it is as I wrote: I set the temperature on CO. e.g. 70 degrees C - the boiler heats the water in the system perfectly to the set 70 degrees Celsius, the flame modulates beautifully during heating (it has always been like that). After reaching the setting, the flame decreases to the minimum and it's supposed to be OK, but after about 5 minutes I see the CO temperature rise above the setting on the display, i.e. 71, 72, and after a while it shows the L3 symbol (the boiler has reached 73 degrees C in the manual (i.e. by three degrees above the set temperature).
I am not a specialist, I am writing what I have observed. What can I set the temperature I want - it is always the same.
One more thing - this morning I swapped the NTC sensors - CO to DHW and vice versa - for peace of mind, the effect - no change. They have the same parameters, so I didn't risk anything.
I think I have described everything ...

This is the correct operation of the boiler. L3 - exchanger cooling, the boiler has reached the set temperature, e.g. 70 degrees, but the environmental sensor (room thermostat) has not yet sensed the appropriate temperature in the air, so the boiler continues to operate (pump) and turns on the burner, heats it to the limit desired temperature and turns off the burner. long until the environmental sensor disconnects it. If there is no such sensor, it works in such cycles all the time until the user turns off the boiler. If the manufacturer did not provide for such a solution, the temperature after heating the central heating system would increase until the burner was turned off by the limit temperature sensor. A very fast temperature rise and the L3 code may indirectly indicate the lack of adequate flow in the installation (filters, valves), otherwise it is normal boiler operation.
greetings

Hello,
Buddy, you descaled the exchanger, and did you check the flow on the outlet pipe?
I had the same problem, I cleaned the exchanger and the inlet and outlet pipes especially, and the problem disappeared. The stove works sensational. I will say otherwise, there was even more sediment on the tube than in the exchanger. I did not expect either, and yet.
Write if it was successful.
I give you

I had a similar problem, the problem was a broken three-way valve.

Hello!
I have a card with NTC 33 and it's damaged NTC 33 I want to replace it but I can't because in my country I can't find it.
How can I replace it with an equivalent?