gas filter buggy

Please double check if there is no connection between orange and green port of your right filter. The new overlay is misleading, because it hides such connections. I would suggest you dismantle the pipes, and rebuild it carefuly and check again.

I didn't spot any pipes there but dismantel the filter and setting it up anew worked. Many thanks!

Thats the problem. If you shorten the ports you wont see it, because KLEI messed up the overlay with the last major patch, and pipes (rails...) vanish behind the buildings. 

I had a similar issue of yours, but in my case the gas filter is working at all. It is working more like a gas bridge. The filter is simply not working despite the game still informing that the filter is "nominal". The selected gas on the filter still leaving trhough the output for non-filtered gas, while the filtered gas output is literally empty. I'll try to dismantel the gas filters also and if stills not working so I'll open a new topic about this bug.