Leak Testing Before First Boot

Leak testing is the step that separates a small inconvenience from a dead motherboard. Do it before any component other than the pump has power.

How to leak test:

1. Fill the loop with the rest of the system unpowered. Only the pump should receive power during testing — most builders bridge the power supply so the pump runs while nothing else does.
2. Run the pump and top up the reservoir as air clears and the level drops.
3. Lay paper towel or plain kitchen roll under every fitting, joint and port. A slow weep is invisible against black tubing but obvious on white paper.
4. Leave it running for several hours — overnight is better. Slow leaks at a compression fitting can take hours to show.
5. Check every joint by eye and by touch before you declare it dry, paying particular attention to fittings you had to tighten at an awkward angle.

Test again after a heat cycle: Tubing and fittings move slightly as the loop warms up and cools down for the first time. A loop that was dry during a cold test can weep at a fitting after its first proper heat cycle, so check joints again after the first day of real use.

Common leak points: Compression fittings that were not fully seated before the collar was tightened; O-rings pinched or rolled during assembly; ports where a fitting was cross-threaded; and drain valves left slightly open. Hand-tighten fittings firmly, but do not use tools to force them — overtightening damages O-rings and causes the leak it was meant to prevent.

If you find a leak: Power everything off immediately, drain the affected section, and let all components dry completely before applying power again — a day is not excessive. Do not power a wet system to "see if it still works".

Hard tubing in particular: Bends that are under tension because a run is slightly too short will pull against fittings over time. If a tube has to be flexed into place, remake it rather than relying on the fitting to hold it.