7.11 The ten most common installation mistakes
Key idea: Most early heat pump failures come from a short list of avoidable installation mistakes.
Learn this list and check it on every job. Each mistake has a clear symptom and an easy prevention.
| # | Mistake | Symptom | Prevention |
|---|---|---|---|
| 1 | Unit boxed in, outlet facing a wall | Low output, frequent defrost, icing | Respect clearances; keep outlet path clear |
| 2 | Pipe too small for the flow | High-pressure or flow trips, noise | Size for 0.7–1.5 m/s; do not copy unit stub size |
| 3 | No strainer, or never cleaned | Low flow, blocked plate heat exchanger | Y-strainer on return; clean after first week |
| 4 | Air trapped in the circuit | Gurgling, pump noise, flow alarm | Air vents at high points; bleed after first run |
| 5 | Expansion vessel missing, wrong size or flat | Safety valve dripping, pressure swings | Size from system volume; check pre-charge |
| 6 | Brazing without nitrogen | Blocked expansion valve, compressor failure | Always flow OFN while brazing |
| 7 | Poor vacuum / no decay test | Moisture, acid, high discharge temperature | Micron gauge, 500 microns typical, decay test |
| 8 | Wrong charge (by guess) | Low COP, high or low pressure trips | Charge by weight per manual |
| 9 | Weak supply, no earth, wrong phase sequence | Trips, burnt terminals, reverse-running compressor | Proper cable, MCB, RCD, earth, phase check |
| 10 | No or poor insulation and no UV cover | Heat loss, sweating, foam crumbling | Insulate fully; clad outdoors |
Commissioning record (minimum)
Record these values at handover: supply voltage, running current, flow and return temperatures (TT-1, TT-2), system pressure (PT-1, PT-2), strainer pressure difference, refrigerant charge (split units), earth resistance and insulation resistance. Leave a copy with the customer.
Remember
- Clearances, pipe size, strainer and air vents fix most water-side trips.
- Nitrogen, vacuum and weighed charge fix most refrigerant-side failures.
- Earth, protection and phase sequence fix most electrical failures.
- Record commissioning values; they are your baseline for future service.
Field tip: Revisit after one week: clean the strainer, bleed the air and recheck pressure. It prevents most callbacks.
Most early heat pump failures come from a short list of avoidable installation mistakes.
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