Vaillant CO Gas Stove: Loud Buzzing/Humming from Upper Part (13yr old) - Repair or Replace?

Hello,
today my central heating furnace started to roar horribly while heating.
It is a British Vaillant stove, about 13 years old. The stove heats one circuit - hot water in a 150l tank and heating the house (radiators). The water/heat changeover is done by a valve.
I hear the roar coming from the upper part of the stove, where the fire is. It's definitely not the pump, because after turning off the heating (reduced to a minimum), the pump still runs a little and does not make such a sound.
The roaring is so loud that it can be heard loudly 2 floors above.
I recorded it but be careful with your ears:

As you can see, the water pressure is correct, I recently bled the radiators and poured anti-corrosion agent into the circuit.
I am asking for advice, whether I need to replace the furnace, whether a visit to the gas fitter is enough, or is it some trifle that I could deal with myself.
Thanks in advance for your help.

Maybe something wrong with the circulation pump? I also had a similar problem, the stove was getting louder as the heating progressed. The radiators were bled but the stove itself was aerated. The plumber unscrewed something in the stove, drained the water, poured it back in and subtracted it with his hand.

I wrote that it's not the pump because after turning off the burners, the pump continues to run and does not make noise.
About a month ago, I drained all the water from the circuit and bled everything.
The pump itself which is located in the furnace has an automatic vent valve, I suspect that it does not work because it is all collapsed. However, when I drained the water from the circuit, the stove got air (above the pump) but there was no roar, only gurgling and a little louder work (nothing compared to what is now). Then I vented several times on the valves at the water tank which is located one floor above and in the upper radiators.
I checked again a while ago, and it's not always like that. It heats for a few minutes normally without noise and only after a few minutes it starts to roar, but the noise is almost unbearable.

Blower to be checked. In a worse scenario, a flue gas installation.

is it atmospheric or turbo? how to check the turbo fan you can also listen to the coil of the gas fittings, but when it hums, it makes a sound of a slightly different frequency.

I don't know if it's a turbo but it says "fan assisted system boiler", it's a THERMOcompact model but the instructions are the same for the TURBOcompact.

Indeed, the sound matches the fan, a few days later it already sounds different:



The instructions are in the attachment.
From what I can see there is a fan on top of the stove.
Advice on how to take it apart? You will need to remove the entire furnace casing and disconnect the exhaust pipe:



Are there any sensitive components and it's better to have a gasser do it? (I seriously doubt). Will it be a matter of cleaning the fan or are any bearings failing there?

As far as I remember disassembly was not a problem. I do not know your manual skills, so if you have any doubts, ask for a visit from a service technician. Something could have just fallen into the fan, and if not, the service technician should diagnose faster if the fan is suitable for replacement.

Thanks. I have abilities, it gets worse with time, but I'll take care of it.