Sounds like the hose to the washing machine is either clogged or it is very small. If the output of the pump is restricted it will cycle on and off continually. You should be able to duplicate the problem by turning on your shower to just a trickle and the pump should do the same thing. I would check/replace the hose, but if your work around is working and the washer is filling properly I'd continue as is. It won't hurt anything and, in fact, is easier on the pump because its not starting and stopping all of the time.

When you are on the mains water does your washing machine work OK?

Yes, turning the shower pressure low replicates the on/off cycling.

The clothes washer usually works on the mains, but sometimes the pressure is too weak and it gives an error for no incoming water. It's strange when the pump goes into the on/off cycling the clothes washer does not show an error, but continues on with it very dry inside.

The reason that the pump cycles on and off quickly is due to the size of the accumulator tank on the pump. With a tap fully open the pump runs all of the time. With it opened just a little, restricted flow, the pump will turn on until the pressure switch turns it off. Then it turns back on when the pressure falls below the lower limit. Since the tank is so small this happens very quickly, therefore on/off/on off .... Opening another tap increase the output and the pump will runn continually. That's the way that they are designed.

After more experience it just works like a champ. I determined only the very first few minutes of the clothes washer cycle needs constant pressure which I achieve by turning on the vat tap. From then on the rest of the cycles need no assistance. Showers are powerful. Two taps can be opened at once without starving the other. Very nice system. Here is what this simple solution looks like for anyone contemplating something similar.

It works as follows: with the switch off water is from the mains as usual. Turn on the switch on and water is drawn from the vat and supplied to all fixtures.

The red numbers are the system components added:

1. junction box to tap into power

2. switch and outlet for pump (pump warranty is voided if plug is cut off and wired directly)

3. all plumbing fixtures should have a shut off valve

4. check valve. In hindsight this is not needed at all as the pump performs this function already.

5. pump

6. intake with foot valve 4 inches off the bottom so as not to draw sediment

7. (not shown) check valve at water meter so pump does not send water to village.