We used two types of check valve, if you have a flat donut shaped one made by RENA, this is overly restrictive and should be replaced, the new one looks like the Tetra check valve but is blue. I can send you a replacement if this is the case. The pump is not servicable, it is unfortunately an expendable part. Basically it uses a 9V dc motor with a direct drive shaft through a rubber seal. Once the seal goes, thats it the motor is broken. They cost less than $17 though. The straining of the motor is not going to shorten its life, only caustic materials that would damage the rubber seal can do this. Some of the problems with the website are language/translation issues. For example the catalogue says in the back under the SKU- Nominal Charge $3.00, an exact translation of the German would yield, $3.00 to be refunded on first purchase, their is no concise way to say this in English. News also has more meanings as a word in German, it can mean details, updates. This is a bit of a problem, English is actually the second best technical Language, German is a language that can be very concise and blunt with few words through alot of prefixes and suffixes. Both Website and catalog layouts only allow so many characters for each spot in a given font, this creates a bit of a problem and frequently we have to use a word that does not have all the meanings it would have in German.