Please help! Boiler (glow worm fuel saver 50B mk II) is performing fine for central heating, but won't fire up for hot water. Pilot light is staying on nicely, it just won't go whoomph for HW. I bought and installed a new programmer, as the old one seemed stiff and worn out, but this hasn't helped. Any suggestions as to what I can try? Thermostat? I'm a carpenter, not a plumber, so no tech speak please. Only bought the house in april! grrr.