My Clarke air industrial compressor wont start sometimes, but sometimes it does??

by Matthew fricker


I have a Clarke air industrial 150l piston compressor that’s about a year and a half old, its worked perfectly until today.

We noticed earlier that it was starting sluggishly, now it starts sluggishly sometimes and works fine, other times it turns once and the overheat switch cuts in and stops it, then it continues to do this for a few mins till it eventually starts fine again.

A new Clarke air industrial 150l air compressor
A new Clarke air industrial 150l air compressor

It cant be the cold as winter where i live has barely set it yet, and it ran last winter fine. Its wired in the same way it has always been and has Always worked fine.

I just cant understand how it works sometimes and not others. I would just like to add that it still starts sluggishly even when it does work and the psssshhhht sound is heard when it fills up.

It also doesn’t work more times than it does.

Please help as soon as you can as im really stuck and i run a small car repair centre ( and we have a van to paint by end of week and this is my only compressor as the other 200l is dead too 🙁

Thanks, Matthew

Matthew, no change in power supply, nothing else pulling power from the same circuit sometimes when the compressor is trying to start? Make sure the power source is clean.

Turn off the compressor, dump all the air from the tank, close the tank drain, and start the compressor. Any change? If it starts fine with no air, I suspect a sticking unloader valve or perhaps the pressure switch is not tripping fully or properly, and the unloader isn’t getting opened every time, or full power isn’t flowing to the motor when it is supposed to.

Next guess… start capacitor, though I would expect that to be a constant problem rather than intermittent if it was failing.

Give us some feedback as a comment, please.


by: Matthew

No change to power supply or anything added or taken away but have noticed a small valve on the heat sink on the pipe that goes out from the pistons into the tank that seems to be sticking and making more noise than it used to.

I assume that this valve opens when the compressor starts to allow airflow into the tank and closes when it stops to keep it in the tank. I would assume then that if it sticks closed on startup then the compressor is overloaded and it cuts out.

I also assume that the sluggish startups that work are sluggish as the valve is slow to open. I want to check the next time it cuts out if the valve has opened and if it hasn’t then i would say that’s the prob. However it hasn’t failed yet today so until it does i cant say.

If this does turn out the problem can i fix it? Is it OK to unscrew it and clean and oil it just i don’t want to break it.

Thanks for all your help.


Before doing any work on the compressor, unplug it, and drain all the pressure from the tank. Then, fill your boots. Enjoy!

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