ᐅ Vitodens 100 – Brainstorming for Replacing a Faulty Heating System

dertill schrieb:

I would estimate the cost of replacing the Viessmann heat exchanger at around €2000 (about $2200), assuming you find a professional and the material is available. It might be significantly cheaper, though; 3-4 years ago it was more like €1000 (about $1100), but prices have changed since then.

If water only leaks during operation and the heating system continues running without errors or pressure loss, it is probably condensation water. In that case, the heat exchanger has corroded through somewhere around 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, it would usually be replaced with a new one. If you do not live in Baden-Württemberg or Schleswig-Holstein, I would recommend ordering a new gas boiler with the mentioned buffer tank soon, and also take advantage of the renewable-ready funding from the BEG program, even if the full implementation with solar panels is not yet feasible.

Apparently, the heat exchanger is no longer available new from Viessmann, which is why many heating technicians hesitate to take on the job.

The heating system is running without errors so far and shows no pressure loss, correct. I definitely want to do something about it, but it is still operational. That means we have gained some time to make a final decision on how to proceed. At the moment, I am thinking we will simply install a new gas boiler.

Then you should hurry, as dertill already mentioned. In Baden-Württemberg and Schleswig-Holstein, it is already no longer allowed, and nationwide the installation will be effectively banned starting in 2025.

We faced the same decision. Originally, the old gas heating system was supposed to keep running until we improved the house’s energy efficiency enough to install a heat pump. However, due to a malfunction in the control unit and several reliability issues, we finally bit the bullet and had a new condensing boiler installed. Now we can renovate at our own pace and see how low we can get the flow temperature. Based on that, we will eventually decide whether an air-to-water heat pump makes sense. At least during the very cold week in December (-13°C / 9°F), we managed with 55°C (131°F) and used less energy than with the old heating system at +10°C (50°F). So far, we have replaced windows, partially exchanged radiators, and insulated the loft with 20 cm (8 inches) of insulation rated WLG 035.

The next project is insulating the gable wall (90 sq m / 970 sq ft) with 14 cm (6 inches) of insulation rated WLG 035, which is currently the biggest weak spot.

Buschreiter schrieb:

We faced the same decision. Ideally, the old gas heater was supposed to keep running until we improved the house’s energy performance enough to install a heat pump. However, due to a control system failure and several reliability issues, we eventually bit the bullet and had a new condensing boiler installed. Now we can renovate calmly and see how far we can lower the flow temperature. Based on that, we will eventually decide whether an air-to-water heat pump makes sense. At least during the freezing week in December (-13°C (9°F)) we managed with 55°C (131°F) and used less energy than with the old heater at +10°C (50°F). We upgraded windows, partially replaced radiators, and insulated the attic with 20cm (8 inches) of insulation with a thermal conductivity rating of 0.035 W/(m·K).
The next project is insulating the gable wall (90 sqm (970 sq ft)) with 14cm (6 inches) of insulation rated at 0.035 W/(m·K), which is currently the biggest weak point.

That sounds very pragmatic!
Are you doing the exterior insulation yourselves?
Thanks!

We will hire a company to carry out the insulation. The energy efficiency consultant gave me the ID for the funding application to BAFA yesterday, and the application has already been submitted. In my experience, it can take a while until the funding approval letter arrives (for the windows, about 5 months!). We already have two quotes. The first offers the same service at €230/sqm (approximately $245/sqft), the second at €165/sqm (approximately $177/sqft). Both are experienced and reliable contractors based on past experience. A third quote is expected later this week.

By the way, according to my calculations, the new gas heating system will pay for itself in about 7-8 years!