Exactly 5 years ago I bought a Diamondback Recumbent Exercise Bike (Model 400Rb) but a few months ago (well, quite a few actually) it developed a problem where the resistance is now much higher than it should be and even the lowest setting is now very difficult to pedal. 
I’ve been doing some Googling to see what the problem might be and have found some very helpful articles.
Exercise Bikes & Electromagnetic Problems
The Reliability of Magnetic Resistance Exercise Bikes
How to Repair the Magnetic Resistance for Exercise Bikes 
!!
When my bike started playing up I thought it might be the batteries in the control panel so I replaced them, but that didn’t make any difference so I haven’t been using it much because it’s too difficult to pedal. So, now armed with more knowledge about the beast, I can set about attempting to repair it myself, based on the info I found online …woohoo! I wasn’t looking forward to having to pay for repairs, plus transporting the thing to wherever to have it done. Hopefully this will work! I’ll report back here eventually when I’ve had a chance to try repairing it.
