ᐅ Vitodens 100 – Brainstorming for Replacing a Faulty Heating System

Hello,
We are currently buying a house, and the installed Vitodens 100 8-24 kW boiler has a leaking heat exchanger. The seller reduced the purchase price by €9,000 based on a quote for the repair. So now I have to take care of it.
Apparently, condensate is leaking. The heating system itself is still running without any failures. There is just a bucket underneath it now and a small drain installed.

• Built in 1965
• Heating system from early 2003
• Some radiators are old and urgently need to be replaced
• Vitocell 100 as domestic hot water tank
• 25,000 kWh gas consumption so far (likely to decrease now as fewer occupants and some insulation measures are planned)

Is it possible to repair something like this again?
Does it make sense to switch to a heat pump?
Would you simply install a new gas boiler with a buffer tank, preparing for a stove and solar thermal system?

I appreciate any input, thank you!

A proper assessment of the existing condition is important now. You obviously want to renovate as well. What exactly do you want to renovate, to what extent, and how much budget is available for this?
Are there any considerations regarding climate protection? How many radiators are installed, 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 @Joedreck, I would think further... so I would involve an energy consultant. Preferably not one who only obtained the certification in an evening course as a technician on the side, but someone who professionally already has knowledge of building physics, such as a civil engineer or an architect. Which region are you from? In North Rhine-Westphalia (NRW), I could recommend our architect and energy consultant.

At the same time, the energy consultant should, no, must also show which funding options are available in order to potentially finance more than the costs themselves.

jrel1238 schrieb:

The Itodens 100 8-24 kW is leaking at the heat exchanger. The seller has discounted €9000 from the purchase price based on an offer. So now I have to take care of it.
Apparently, condensate is leaking. However, the heating system is still running without any faults.

I would estimate a Viessmann heat exchanger replacement at around €2000, if you can find someone and have the material available. It might even be significantly cheaper; 3-4 years ago it was closer to €1000, but that doesn’t mean much today.

If water only leaks during operation and the heating system continues running without errors or pressure loss, it’s condensate, and the heat exchanger has likely corroded through at the mounting points due to microcracks or something similar. This definitely needs to be fixed and cannot be ignored.

Given the age of the heating system, normally you would install a new unit. If you don’t live in Baden-Württemberg or Schleswig-Holstein, I would recommend ordering a new gas heating system with the mentioned buffer tank soon and taking advantage of the renewable-ready funding from the building permit / planning permission subsidy, if it’s currently not enough for a full solar installation.

Joedreck schrieb:

A proper assessment of the current condition is important now. You obviously want to renovate as well. What exactly do you want to renovate, to what extent, and what budget is available?
Are there any concerns such as climate protection? 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, with smaller energy-related improvements like insulating the roller shutter boxes (and switching to electric), renovating the bathroom, etc. The gas heating system is currently failing, which raises the question of what to do next.
Three radiators need to be replaced; there are about 14 radiators in the house overall.
There is a basement that will be waterproofed and insulated with perimeter insulation. I don’t plan to do anything further there for now. The top floor attic is insulated with 10cm (4 inches) of expanded polystyrene.
Some exterior walls are partially covered with expanded polystyrene and drywall panels.

i_b_n_a_n schrieb:

Not a direct answer to the question, but like @Joedreck, I would think further… so consider consulting an energy consultant. Ideally, not someone who just took a technical certificate course in the evening, but a professional with solid knowledge of building physics—such as a structural engineer or an architect. Where are you located? In North Rhine-Westphalia (NRW), I could recommend our architect and energy consultant.

At the same time, the energy consultant should, no, must also clarify which subsidies or grants are available to hopefully more than cover the costs themselves.

The energy consultant is coming this week. He is indeed also an engineer and a structural analyst. I am located in Hesse.