ᐅ Repair a heat pump for €5,000–7,500 or replace it with a new one?

Hello dear forum members,

we are facing the decision of "repair" or "new heat pump" and would appreciate your opinions.

Our 7.5-year-old heat pump has broken down after 68,000 starts in 7.5 years (25 starts per day).

Problem with the heat pump:
- The cause of the frequent cycling is unclear. (Most individual room valves are fully open.)
- The only available customer service is the German distributor (400 km (250 miles) away)
- The heat pump is oversized at 3-12 kW; 7-8 kW would be sufficient according to calculations
- The hot water tank is somewhat small at 165 liters (44 gallons) for 5 people

Possible repair appointment:
- Compressor replacement €5,000 (including installation)
- Fault diagnosis (dirt trap in the heating circuit/brine circuit?, temperature sensors?, bypass valve?)
- Possible control system optimization (improving speed regulation to enable lower speeds? possible speed limit? night setback? high hysteresis? possible blocking times?)
- Optional retrofit of a buffer tank (€2,000 plus installation, no combination buffer possible)
- Risk that the frequent cycling persists afterwards

Alternatively, we could install a new heat pump:
- Change to a larger manufacturer with a better service network
- Several weeks without hot water (the current electric heater only heats the water to 32°C (90°F)) until new installation
- New 5-year warranty
- Unknown costs, probably very expensive

(1) What do you think a new heat pump including installation would cost?
(2) How long do you think the installation would take?
(3) What are your thoughts on the repair vs. replace decision?

Additional data:
Location: Budenheim near Mainz

Current broken heat pump: Ecoforest geothermal heat pump (Model C3 3-12 kW HTR EH), modulating 3-12 kW, connected to underfloor heating and two 100-meter (330 feet) boreholes. Hot water tank 165 liters (44 gallons).
It was probably oversized at the time. The calculated optimal size is 7-8 kW.
The compressor failed after 68,000 starts in 7.5 years (25 starts per day). Two neighbors have the same heat pump in similar homes (same construction company) with 5 starts per day. Customer service at Ecoforest is poor.

The heat pump’s annual balance shows:
Heating 12,740 kWh
Cooling 1,850 kWh
Electricity 3,180 kWh
Annual performance factor (COP): 4.6

Additional data:
Energy standard: nearly KfW-55
Annual primary energy demand Qp according to energy-saving regulations: 34.5 kWh/(m²a)
Specific transmission heat loss H’T: 0.305 W/(m² K)
Heated building volume 920 m³ (32,480 ft³)
Living area: 220 m² (2,370 ft²)
Heated living area: 170 m² (1,830 ft²)
Household: 5 persons
Controlled mechanical ventilation installed
9.9 kW peak photovoltaic system installed

Desired heat pump:
- Modulating heat pump
- Capacity smaller than current (3-12 kW)
- Larger hot water tank than current (165 liters (44 gallons))
- Passive cooling function
- Electric backup heater for emergency operation
- Connection for 10,000-liter (2,600 gallons) basement pool (max 31°C (88°F)) possible (currently connected via low-temperature heat exchanger to heat pump)

jx7 schrieb:

Desired heat pump:
- Modulating heat pump
- Capacity smaller than before (3–12 kW)
- Hot water tank larger than before (165 liters)
- Passive cooling function
- Electric heating element for emergency operation
- Connection for the 10,000-liter (2,642-gallon) basement pool (max. 31°C (88°F)) possible (currently connected via low-temperature heat exchanger to the heat pump)

If you hadn’t just started the last thread and already had a borehole (for passive cooling), my advice would have been:
Take a weekend, buy a 7 kW monoblock today (which will then be delivered early next week for under €4,000) and connect it.

But a brine-to-water heat pump is a bit more complicated, and you’ll have to plan for delivery times and tradespeople availability. Difficult situation.
Let’s first look at your heating load calculation:
- Postal code unknown
- Building envelope area unknown
- Desired room temperature unknown
- Type of ventilation unknown
==> I roughly estimated everything
==> I therefore see a 5 kW heat pump for you, possibly a 7 kW one that modulates low enough.

The decision will largely depend on when you can get a new heat pump (that would be my first choice).

jens.knoedel schrieb:


- Postal code (ZIP code) is unknown
- Building envelope area is unknown
- Desired indoor temperature is unknown
- Type of ventilation is unknown

Thank you very much for your response!

Here are the missing details!

Postal code (ZIP code): 55257
Building envelope area: unknown
Desired indoor temperature: 22.5°C (72.5°F)
Ventilation: Mechanical ventilation with heat recovery

@jens.knoedel
Where did you find this calculator? I would also like to run my house through it. I see myself in the same situation as the original poster in 5-8 years, since our heat pump was also massively oversized. Because the general contractor consistently refused to deviate from this, we were forced to go along with it. Changing the general contractor for this reason was a choice between the devil and the deep blue sea.

What refrigerant does the old unit actually use? Keyword F-gas regulation? I couldn’t find anything quickly, so maybe the next problem is already lurking there.

You mentioned 60,000 starts in 7 years—how many operating hours?