Looking for help. I have recently moved into a 3 storey house with a combi boiler on the ground floor. The basin on the third floor has plenty of pressure and flow but the flow does not fire the boiler (a Vaillant). If I turn a kitchen tap on low then boiler fires and the water upstairs is hot.
I am baffled, since the flow is good, why the boiler does not fire. Any ideas? Is the flow switch adjustable? It beats me.