Overheated Yong Heng

If it's not building pressure. Most likely the high piston rings are damage and need to be replaced.

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If it is not building pressure but the sound of running is still normal then there is probably no structural failure but some of the seals has been damaged. I will start by replacing all the seals in the first stage, second stage and the O-ring of the check valve inside one of the stainless tube connectors along the output of the first stage. The good thing about Yong Heng is that the construction is simple and parts are readily available so you can service it by yourself. If your Yong Heng is a genuine one, make sure that you get the original Yong Heng parts or they may not fit.