Unusual airlock

[jinja]

I have a direct feed electric shower that has always, for a few years now, worked perfectly, until a short time back when a nearby farm had to start irrigating in the mornings. They have stopped doing this now.

When they were irrigating this seemed to affect our water pressure (our house was once the property of the farm) and the water came very erratically through the shower (with massive changes in temperature!). However, the water continued to flow ok through all the other taps in the house.

The water supply to the shower comes from the general pipework near to the tank and is not directly in line with the pipe supplying either the bath or the hand basin.

This has never happened before but now, when running the shower the water just dribbles out of the showerhead, accompanied by screeching. But, if I turn on the cold tap of either the bath or the handbasin this immediately releases the full pressure through the shower.

It seems to be a sort of airlock but I can't figure out why the air bubble, if it is one, hasn't been blown out once the shower is operating at full tilt?

Anyone got any ideas why this situation has arisen, and more importantly, how I can correct it?

 

[Nige F]

could be a micro switch in the shower on the cold supply

 

[kisoro]

I haven't opened up the control panel because the shower works off the mains supply of cold water, therefore I think it unlikely there would be a cold water switch and I don't remember seeing any such switch when I installed the unit originally.