Third top-up in a year: the pipe run settled it

Three top-ups in one year is not a gas problem. It is a leak problem, and the leak has an address. Finding it changed the question from what to top up to what to replace.

By Team Snowflake | Reviewed 25 Jul 2026

Case summary

LG Multi-split15 years oldHDBPasir Ris, Singapore

Concern: Three separate visits had ended in a gas top-up, each one billed, none of them lasting past a few months.
Found: Pinhole corrosion at more than one point along the original pipe run, which no further top-up could hold
Key check: A held test on the isolated pipe run, which lost pressure with both units disconnected
Result: Gas has held since the new system and pipe run went in. No further top-up has been called for.

What we were told

Cooling faded a few weeks after each service visit, and the same fix followed every time. The bedrooms went warm first, then the living area. The most recent top-up held for barely two months before the rooms started feeling humid again. No leak test had been done on any of the three visits.

What we checked

A leak that comes back needs to be located, not refilled. We isolated the pipe run from the indoor and outdoor units and held it under test on its own. That splits the system into parts that can be judged separately. If the run holds and the units do not, the fault is at an end fitting. If the run drops, the pipe itself is the problem.

The isolated pipe run lost pressure steadily with both ends disconnected.
Bubble testing along the exposed sections found weeping at two separate points, well apart from each other.
The pipe insulation had split and gone hard in several places, leaving the copper open to damp air for years.

What we found

The copper had corroded from the outside in, at more than one point along a run that had been in place since the flat was fitted out. Split insulation let damp air sit against the pipe, and the sea wind across this estate kept it salty. Two weeping points were found and there was no reason to think they were the last. That is what made further top-ups pointless. Each one was paying to fill a pipe that had stopped holding.

What fixed it

Patching two points on a pipe run of that age does not end the cycle. We priced a full replacement of the system with a new pipe run, and set it against the alternative of repeat visits with no end date. The indoor and outdoor units were the same age as the pipe and had their own wear. Replacing the pipe alone would have left worn equipment feeding a new run.

Outcome

Gas has held since the new system and pipe run went in. No further top-up has been called for.

What this case teaches us

Repeat top-ups are a bill, not a repair

Gas does not get used up. If a system needs topping up again, something is letting it out and that point can be found.
Ask for a held pressure test with the units isolated. It separates a pipe fault from a fault at either end.
Old pipe runs corrode from the outside in. Once the leaks come in more than one place, patching stops being the cheaper path.

Questions this case answers

Why does aircon gas keep running out after every top up?

Because a sealed system does not consume gas. If it needs refilling, something is letting it out, and that point has a location. Three visits to this Pasir Ris flat each ended in a top-up with no leak test, so nothing was ever found. The most recent one held barely two months before the rooms went humid again.

What test should be done before agreeing to another gas top up?

A held pressure test with the pipe run isolated from both units. That splits the system so the fault can be placed. If the run holds and the units do not, the leak sits at an end fitting. Here the run dropped steadily with both ends disconnected, which put the fault in the copper itself.

Can a leaking aircon pipe be patched instead of replaced?

One leak on otherwise sound copper can be repaired. Two on an old run is a different picture. Bubble testing found weeping at two points well apart on this pipe, with insulation split and hardened along several stretches. Nothing suggested those were the last two, so patching them would have bought another round of the same visits.

Does living near the sea affect aircon pipework?

It does, and this estate sits close enough for it to matter. The insulation on this run had split and gone hard in several places, leaving bare copper against damp air. Salt in that air speeds the corrosion, which works from the outside in until the wall thins to a pinhole. Intact insulation is what normally prevents it.

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