Ductless mini-splits are a natural fit for Mill Valley homes without ductwork, and many houses in town, including those near Muir Woods, now run one or several. Because they are heat pumps, they work most of the year here, heating rooms that stay cool and damp under the trees. That steady use, plus moisture, explains most of the repairs we do: drains that clog, indoor units that grow a film on the blower, sensors that drift, and outdoor units that ice up when defrost fails.
Start with the error code
Most mini-splits report faults with a code on the indoor unit’s display or a pattern of blinking lights. Before you call, write down the code, which indoor unit shows it and what the system was doing at the time. That narrows the diagnosis before we arrive, and we send a technician familiar with your brand.
Common mini-split problems in damp homes
| What you see | Likely cause | What it usually takes |
|---|---|---|
| Water dripping from the indoor unit | Drain line clogged with slime, unit out of level or a failed condensate pump | Clear and treat the drain, re-level the unit or replace the pump |
| Weak airflow, musty smell | Dirty filters and a blower wheel coated with growth | Deep cleaning of the coil and blower wheel |
| One zone works, another does not | Communication fault, wiring, or a failed indoor board or sensor | Zone-by-zone testing and the failed part |
| Cool air in heat mode | Defrost cycle, low charge or a sensor fault | Check defrost, then a leak search if needed |
| Outdoor unit iced solid | Defrost sensor or control failure, or a coil packed with debris | Clean, then test the defrost controls |
| Runs but never reaches the setting | Low refrigerant from a leak, often at a flare joint | Find and repair the leak, then recharge |
| Remote does nothing | Batteries, or the unit set to an unexpected mode | A quick check before any repair |
Leaks at flare connections are one of the most common mini-split faults. Topping up the refrigerant without fixing the joint only buys time, so we find the leak first.
Testing every zone
A multi-zone system can hide one problem behind another. One indoor unit with a failed sensor can change how the outdoor unit runs for every room. So we test all the zones, not only the one you called about: each indoor unit’s airflow, temperatures, drain and sensors, and the outdoor unit’s charge, fan, defrost and electrical parts. When the repair is done, we run every zone again to confirm the whole system works.
How the visit works
- Report the symptoms: the code, the affected unit and what it is doing.
- Technician dispatch: someone familiar with your brand.
- System testing: every zone and every component.
- Repair recommendation: we explain the problem and give you the price.
- Repair: we fix it and verify that all zones work.
Repairs carry a 90-day warranty, and same-day service is available for most calls.
Keeping it running
Pick a comfortable temperature and leave it there: inverter units do their most efficient work holding a steady setting rather than being switched off and on through the day. Rinse the indoor filters every few weeks in heavy use, keep the outdoor unit clear of needles, and have the coil and blower wheel cleaned once a year.
If the system is old and failing, see mini-split installation in Mill Valley. Ducted heat pumps are covered under heat pump repair. For more detail on ductless repairs, see our mini-split repair page, and for the rest of our work in town, the Mill Valley page.