Bosch’s home heating and cooling range is built around inverter heat pumps, often fitted in place of an old air conditioner on a house’s existing ducts. When one in Menlo Park, Atherton or Portola Valley stops heating or cooling, the cause is more often electronic or sensor-related than the worn contactor or capacitor of an older single-speed unit, and the outdoor unit’s control board usually keeps a record of what went wrong.
What Bosch makes
- Inverter ducted heat pumps, sold as IDS (Inverter Ducted Split), which connect to a furnace or air handler and the existing ducts.
- Ductless mini-splits, single-zone and multi-zone, for rooms or additions the ducts do not reach.
- Geothermal heat pumps, which draw heat from loops buried in the ground.
- Gas furnaces and air handlers, the indoor half that pairs with the outdoor heat pump.
How an inverter heat pump behaves
An inverter changes the compressor’s speed to match the load. Instead of switching fully on and off, it runs long and slow most of the time. Two things homeowners report as faults are normal:
- It runs for hours. Long, low-speed run times are how the system holds an even temperature with less energy.
- Steam rises from the outdoor unit in winter. That is a defrost cycle clearing frost from the coil.
What is not normal: a system that shuts down and restarts again and again, blows cool air in heat mode outside a defrost, or shows a fault code on the outdoor board or the thermostat.
What we check, in order
- The fault history. The outdoor control board logs faults. We read it before touching a part.
- Power. Low or unstable voltage, loose connections and surge damage cause many inverter faults, so supply voltage, terminals and the breaker come next.
- Sensors. Temperature sensors on the coils, the lines and the compressor tell the board what to do. A failed sensor can look like a failed board and is a much smaller repair.
- The expansion valve and the charge. Inverter systems typically use an electronically controlled expansion valve, and the charge is set by the maker’s procedure, often by weight.
- The inverter board itself, only once the cheaper causes are ruled out.
An inverter-driven compressor usually has no run capacitor, so the most common repair on older outdoor units does not apply here.
Thermostats and controls
Some inverter heat pumps run from a conventional heat pump thermostat; others need a specific control to reach full modulation. Before changing the thermostat on a Bosch, find out which applies, or the system may keep running but lose its variable-speed behavior. Thermostat installation covers compatibility.
Warranty and paperwork
Keep the installation invoice, the registration confirmation and the model and serial numbers of both the outdoor and indoor units. With inverter equipment, also keep the startup record: line-set length, refrigerant added and the settings chosen at installation. It shortens any later repair and supports a warranty claim. Damage from power surges is often excluded from manufacturer coverage, so a fault right after a storm or an outage may be treated differently from a component defect.
Repair or replace
A sensor, a connection or a fan motor is a repair. An inverter board is a larger one, but on a young system it is still usually the sensible choice; ask about part availability and timing, since electronic parts are not always in local stock. A failed compressor on an older system out of coverage is when heat pump installation comes up. Either way, the diagnosis, parts, labor and options come in writing first.
Local notes
Menlo Park has many older homes being converted to heat pumps next to newer rebuilds, and a Bosch fitted to old ductwork depends on those ducts being sealed and sized for its airflow. In Portola Valley, outdoor units are often set away from the house on a slope or in a quiet corner, which means long refrigerant and electrical runs; those runs have length limits, and a long one deserves a look at the startup record. With winter lows mostly in the 40s on the bay side, a heat pump can usually carry the heating on its own, while Portola Valley’s cooler nights ask a little more of it. For problems, see heat pump repair.