Expert report
The German version is the legal document for a dispute in Germany; this is the same report in English.
The heat pump reaches a seasonal efficiency of 2.74 this year. The reference is 3.0. The system stays below it. 4 of 5 findings concern settings or sizing, the installer's area of responsibility at planning and commissioning.
1 · System and data basis
- System
- Viessmann Vitocal 250-A · Serial –
- Client
- –
- Installer
- –
- Data source
- Example data (PyViCare, recorded)
- Method
- Unit's computed heat balance (manufacturer-reported), not verified against heat meters
- Concern
- Preview without an order
2 · Readings and classification
| Value | Result | Status | Note |
|---|---|---|---|
| Seasonal efficiency (COP), current year | 2.74 | Act | Reference 3.0 · Score 50/100 |
| Electricity, current year | 4,886 kWh | Previous year 7,592 kWh | |
| Heat delivered, current year | 13,407 kWh | Unit's computed heat balance (manufacturer-reported), not verified against heat meters | |
| Excess against the reference | 423 kWh · about 106 € a year | Act | at 0.25 €/kWh; computed from efficiency and yearly consumption |
| Comparison with heat-metered homes | better than 11 % of 139 homes | Reference fleet HeatpumpMonitor.org (UK), yearly values; context, not a yardstick | |
| Heating curve (slope · shift) | 1.1 · +7 | Act | slope very steep |
| Flow / return | 29.8 / 34.2 °C | Info | unit idle now |
| Flow rate | 0.0 l/min | Info | unit idle now |
| Compressor starts per running hour | 3.06 /h | Check | cycles often |
| Hot-water tank | 58.5 °C | Check | very hot: costs efficiency |
| § 14a grid module | 14aOff | Info | discount available |
3 · Indications of causes
The system delivers 2.74 kilowatt-hours of heat per kilowatt-hour of electricity. The reference for subsidies and usual planning is 3.0. Whether settings, sizing or the device are the cause is what the following findings show.
To be produced by the installer: Commissioning record, proof of hydraulic balancing, heat-load calculation and the efficiency named in the quote.The heating curve sets how hot the heating water gets in cold weather. A slope of 1.0 or more is high for a house with radiators and costs 2 to 3 % electricity per degree too much. The installer sets the curve at commissioning and adjusts it after the first winter.
To be produced by the installer: Setting values from the commissioning record, design flow temperature from the heat-load calculation.The shift raises the heating-water temperature in any weather. Values from +6 point to a workaround for another problem, such as an unbalanced heating circuit.
To be produced by the installer: Reason for the shift, proof of hydraulic balancing.The backup heater heats three times as expensively as the heat pump and should only run in severe cold or a fault. A high share points to tight sizing, a wrongly set bivalence point or a fault.
To be produced by the installer: Bivalence point and backup-heater release as set, heat-load calculation, fault log.A compressor that switches on and off all the time uses more electricity and wears faster. Usual causes: a system too large for the house, no buffer tank, too little flow, closed radiator valves. That concerns planning and hydraulics.
To be produced by the installer: Heat-load calculation, buffer-tank sizing, minimum flow rate, minimum run-time setting.4 · Responsibility and legal position
4 of the 5 findings concern settings or sizing, that is, work the installer is responsible for at planning and commissioning: Heating curve too steep (slope 1.1); Heating-curve shift high (+7); Electric backup heater supplied 8 % of the electricity; About 3.1 compressor starts per running hour.
The legal position: after acceptance the customer must prove a defect (§§ 634, 640 BGB). The limitation period is, on the prevailing view, five years from acceptance because the system becomes part of the building (§ 634a (1) no. 2 BGB); there is no ruling from the Federal Court yet. This report documents the state of the system on the reference date from its own data and names the documents the installer should produce. It is a private expert opinion: in court, a court-appointed expert decides and can use this report as a basis.
5 · Recommended steps
- Send a defect notice with a 14-day deadline to the installer and attach this report. The draft is ready under “Letters”.
- Request the documents: commissioning record, heat-load calculation, proof of hydraulic balancing, quote with the promised efficiency.
- After the remedy, wait two cold weeks and have it re-measured; the Heatproof account stays connected for that.
- If no remedy follows: consumer advice centre or a construction lawyer, with this report and the documents.
- Keep the deadline in view: acceptance date plus five years on the prevailing view, two years on the narrower one.
6 · Limits of this report
- Data source: Example data (PyViCare, recorded). Method: Unit's computed heat balance (manufacturer-reported), not verified against heat meters.
- The basis is a snapshot of the settings plus the device's yearly and monthly counters. Hourly history only exists with a live connection.
- The reference fleet consists of British heat-metered homes. Climate and buildings differ; the comparison gives context, it does not measure.
- Not a court expert opinion, not legal advice. The expert confirms the method and plausibility of the analysis, not the manufacturer's readings.
- If the data do not support a statement, the report says so and the fee is refunded.
7 · Co-signature
Licensed expert for refrigeration and heat-pump technology, [Place]
As of 07/11/2026
The co-signature confirms: the analysis follows the published method, the findings are plausible from the data at hand, and the classification into setting, sizing, usage and device matches the state of the art.
Annex · monthly values (kWh electricity)
| Month | Total | Heating | Hot water |
|---|---|---|---|
| Oct 2025 | 69 | 46 | 23 |
| Sept 2025 | 173 | 46 | 127 |
| Aug 2025 | 40 | 0 | 40 |
| Jul 2025 | 59 | 0 | 59 |
| Jun 2025 | 45 | 0 | 45 |
| May 2025 | 93 | 15 | 78 |
| Apr 2025 | 400 | 292 | 108 |
| Mar 2025 | 970 | 765 | 205 |
| Feb 2025 | 1,433 | 1,179 | 253 |
| Jan 2025 | 1,605 | 1,301 | 304 |
| Dec 2024 | 1,490 | 1,192 | 298 |
| Nov 2024 | 1,050 | 796 | 254 |