Depending on the model there will be a few troubleshooting steps we could try.
For the classic series you really want to make sure that your rollers are fully expanded.
If it is an Econ - there is a latch behind the pump head we need to make sure is fully secured.
For anyone interested, I have...
If you are using 1/4" tubing, we suggest the UCAK100 (pk of 10 connecting nuts) and the UCAK200 (pk of 10 ferrules). If you need further assistance, please don't hesitate to contact us here.
We do not suggest using a 'Y' as there is a chance of leaking at the connection. In regards to using the 3/8" tubing, the 1/4" is fine as the pump is a positive displacement pump and increasing the tubing size does not affect the output, unless a viscous solution. I hope this might help.