Gas keeps running out: pinhole leak in pipe behind the wall
Two gas top-ups in one year, and the cooling still faded. Each refill held for a few weeks before the unit went warm again. Nobody had tested the pipe run hidden inside the wall, where the gas was quietly escaping.
By Team Snowflake | Reviewed 10 Mar 2026
Case summary
Panasonic Wall-mounted8 years oldCondoNewton, Singapore
- Concern
- The fear was an internal compressor fault leaking gas, which would mean replacing the whole system.
- Found
- Pinhole leak in copper refrigerant pipe behind the bedroom wall, causing slow gas loss over weeks
- Key check
- Performed pressure hold test on the pipe run to confirm a leak in the concealed section, rather than just topping up gas
- Result
- The gas charge has held steady since the repair, and the repeat top-up cycle has stopped. The compressor stayed healthy throughout, so no replacement was needed.
What we were told
The unit has been topped up with gas twice this year. Each time it cools well for a few weeks, then slowly turns warm again. Two different contractors refilled it and said the gas charge was low. Neither explained why the gas kept running out.
What we checked
Rather than top up a third time, we pressure-tested the pipe run to see whether gas was actually escaping. We held the system under pressure for several hours, checked the joints we could reach indoors and outdoors, and tested the compressor to rule it out.
Under pressure, the reading dropped slowly. The system was losing gas, not just undercharged.
The visible joints at the indoor and outdoor units were tight, so the leak was not at any reachable connection.
The pressure drop traced back to the pipe section hidden behind the bedroom wall.
Compressor checks matched a low gas charge, not an internal compressor fault.
What we found
A pinhole had formed in the copper refrigerant pipe inside the wall cavity. That pipe runs about three metres of hidden space between the indoor unit and the point where it exits the outside wall. Over eight years, moisture in the wall settled on the cold copper and corroded a small spot from the outside in, until it ate right through. The hole let refrigerant escape at a few grams a day, slow enough that no one caught it without pressurising the hidden section directly. That slow rate explains the pattern: cooling held for several weeks after each top-up, then faded as the gas ran low again.
What fixed it
We opened a small section of the bedroom wall to reach the corroded area. The pinhole showed up as a single spot of external corrosion that had eaten through the copper. We cleaned and sealed that section, then pressure-tested the repair to confirm it held. After that, the system was vacuumed and recharged properly. We suggested a recheck at the next service to confirm the repair holds long-term.
Outcome
The gas charge has held steady since the repair, and the repeat top-up cycle has stopped. The compressor stayed healthy throughout, so no replacement was needed.
What this case teaches us
Repeat gas top-ups mean a leak no one has found
- If gas runs out again weeks after a refill, the gas is escaping somewhere. A top-up refills the system but never fixes the leak.
- Leaks can sit in the hidden pipe run inside the wall, not just at the visible joints. Only a pressure hold test on that section will catch them.
- Before paying for a third top-up or a new system, ask whether the concealed pipe was pressure-tested and what the result showed.
Related reading
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