I have a halstead finest gold, 9 years old when trying to run hot taps bath etc, boiler keeps going on and off so takes hours or not at all, seems to help if we put heating on, have been told plate exchanger diverter valve pipes flow regulator electrical? some times runs okay then have days and days when it doesn't we do have scale here, any help please as money tight and wife has disability problems seem to be inbetween for financial help.