Vitodens 100 - Brainstorming for replacing a defective heater

Hello,
we are currently buying a house and the built-in Vitodens 100 8-24kw has a leak at the heat exchanger. The seller has reduced the purchase price by 9000€ based on a quote for this. That means I have to take care of it now.
Allegedly, condensate is leaking. However, the heating system still runs without failures. There is now just a bucket underneath and a small drain installed.

[*]Built in 1965
[*]Heating from early 2003
[*]Some radiators are old and urgently need to be replaced
[*]Vitocell 100 as hot water storage
[*]25000 kwh gas consumption so far (will probably be less now due to fewer people and some planned insulation measures)

Can something like this be repaired again?
Does a heat pump make sense?
Would you simply install a new gas heating system + buffer storage in preparation for a stove + solar thermal system?

I am grateful for any input, thanks!

A reasonable inventory is important now. You obviously also want to renovate something. What do you want to renovate, to what extent, and how much money is available for it? Are there aspects like climate protection in your case? How many radiators are there and how many need to be replaced? What will be insulated and to what extent? Is there a basement?

Not a direct answer to the question right now, but like , I would think further ... that is, consult an energy advisor. Preferably not one who "only" got the certificate in an evening course as a technician on the side, but one who already professionally understands building physics, such as a civil engineer or an architect. Where are you from? In NRW I could recommend our architect and energy advisor. At the same time, the energy advisor should, no, must also show which subsidies are possible in order to ideally finance themselves more than fully.

the itodens 100 8-24kw has a leak at the heat exchanger. The seller has discounted €9000 on the purchase price based on an offer for this. That means I have to take care of it now.
Supposedly condensate is leaking. However, the heating system itself still runs without failures.

Viessmann heat exchanger replacement I would calculate at about €2000, if you find someone and the material is available. Maybe significantly cheaper, 3-4 years ago it was rather €1000, but that means nothing nowadays.

If water only escapes during operation and the heating system continues to run without errors and pressure loss, it is condensate and the heat exchanger has corroded through somewhere at the mounting points due to micro-cracks or whatever. It definitely needs to be fixed, you can’t just let it run.

Given the age of the heating system, normally you would install a new heating system. If you don’t live in BW or SH, I would quickly commission a new gas heating system with the mentioned buffer, and take advantage of the renewable ready funding from the BEG subsidy if the full implementation with solar is currently not possible.

A proper assessment is important now. You obviously also want to renovate something. What do you want to renovate, to what extent, and how much money is available for it? Are there aspects like climate protection for you? How many radiators are there and how many need to be replaced? What will be insulated and to what extent? Is there a basement?

We generally want to renovate the house, smaller energetic tweaks like insulating the roller shutter box (and switching to electric), new bathroom, ... . The gas heating is currently dying, so the question arises what to do. 3 radiators need to be replaced, there are about 14 radiators in the house in total. There is a basement and it is being dried out, with perimeter insulation applied. I wouldn’t do anything else there for now. The attic floor is insulated with 10cm polystyrene. Some of the exterior walls are covered with polystyrene + drywall.

not a direct answer to the question now, but like , I would think further ... so involve an energy consultant. Preferably not one who has "only" done the certification as a technician in an evening course on the side, but one who already has professional knowledge of building physics, that is, a civil engineer or an architect. Where are you from? In NRW, I could recommend our architect and energy consultant. At the same time, the energy consultant should, no must, also show which funding is possible in order to ideally finance more than just oneself.

Energy consultant is coming this week. He is indeed also an engineer and structural engineer. I am in Hesse.