Completely baffled by this problem and hoping someone out there can shed some light. Moved into a new home 8 weeks ago, had boiler checked and everything seemed fine. As of yesterday we suddenly found we had no hot water. We have now discovered that we can still get instant hot water but only if a second source is activated. To give an example, switch the shower on and the water will run cold for days but also switch the hot tap on the sink on and both sources have instant hit water. This isn't an issue upstairs as there are a number of hot water taps in close proximity but having to run upstairs to turn a tap on so that we can get hot water from the kitchen taps is driving us crazy. The hot water light on the boiler will only switch on when a second source is activated no matter what we try. Any suggestions would be greatly appreciated.