On some (if not all) there is also a strainer in teh tank attached to the outlet. Mine had two of 'em ONe was hooked up in front of the actual output line to the pump.. the other was a 2nd port that was plugged (it is now a drain port).
Just so you know. I do not know how common the outlet strainer is. But if it gets "Slimed" up you will get what you got.
2nd: The water heater also acts a bit like an accumulator (pressure tank) and if the pump is simply not up to demands.. Same effect.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times