Bluefish

some of them have lines on them ie, 1 11 111, failing that turn your roomstat up to turn the heating on, then go to the pump and turn the lever and you will be able to tell the differance between the differant speeds, just turn it to a lower speed, if it still happens even when it is on the lowest speed, then yeah you got it, your fecked lol, nah just means it will need more work doing to the system, it's not a mega problem, but every time it pumps water into the tank it's adding more air into the system wich helps cause corrosion and puts air in the rads requiring them to need bleeding more often. Edit, on the cut out portion you refer to there may be the no's written on the lighter part, usually grey coloured, they will be quite small, but as i said you can tell by the noise and feel of the pump wheather it's on it's fastest or slowest setting. once you have finished messing with it it don't make a differance wheather you just turn down the r/stat or turn it off at the programmer, but if you are not going to be using it every day, then i would turn the heating off at the programmer and leave your r/stat at 20 or wherever you usually have it, hth, andy.