Not sure if anybody can help?

I live in Thailand. Our mains water is stored in an external 500 gallon, stainless steel tank and is filtered when drawn from the mains and before being stored. When turning on the tap, water is pumped by an electric pump from the tank into the system and the tank draws water from the mains. Hot water comes from a tank in the loft, and is heated by an electric immersion heater.

Twice in the past couple of weeks we've had the problem that we have no cold water in the kitchen or one of the outside taps; when turning on the tap, the pump does not start and nothing happens. In the cloakroom next to the kitchen and in the upstairs bathrooms, water runs as usual and the pump works as usual. After a few hours, the problem corrects itself.

The local Thai plumber has absolutely no idea what causes this (he would not "lose face" by actually admitting this, especially to a westerner!), thus if anybody has any idea what the underlying problem could be, I'd really appreciate your help.

Hi pigman and welcome to The Plumbing Page at AskMeHelpDesk.com
Up until I read this.
After a few hours, the problem corrects itself. I was thinking sediment night be clogging your supplies but after seeing that it fixed itself about the only thing it could be is airlock. And then I came across this.
when turning on the tap, the pump does not start and nothing happens. which leads me to wonder how the pump switch works. Is this a pressure switch that's activated by a pressure drop when a tap is opened? That's where I would start checking first. The switch's designed to come on when a tap's opened and the pressure falls. Something's not getting through to the switch when you open a kitchen tap. I'd want to know why. Good luck. Tom