Do you know about combi boilers?

Ok ive got a combi boiler.it keaps the house warm but all of a sudden it has stopped heating up the water. Normaly when we turn on the hot tap the boiler kicks in but now it doesnt. the water will only warm up if we turn the taps on full downstairs and the taps on full upstairs. or if we have the heating on and run the tap slowly. any help is greatly received. thanks

[Rich]

Thats the diverter valve.
It might just be the diaghram valve inside the diverter valve(which will cost you about £50 including labour), or if the the actual diverter valve is gone, it will cost you about £170 including labour......but it depends on what combi you have.
I'm not an expert.....but ours went recently.

[Ayub]

the diapram thingy miggy. cost mere pennies from a diy shop!

[Rich]

I checked at a local plumbers merchant beforehand........ours was about £23

[Joany]

before you pay for anyone to come and look at it check out the pressure on the boiler. We had the same problem and the pressure had gone down. Look at the dials on the boiler and make sure they positioned where they should be. If you have already done this apols for trying to teach granny to suck eggs