I used to have a boiler, often gave similar problems, it was down to the way they used to sense water flow, in my case, they used a reed switch in a plastic case, which when water flowed moved the outer component. Used to stick. quick clean all ok. Might find yours is similar, If you are up to it, Open the outer case, look for a couple of wires going to a point on the pipe work within the boiler area, might be a black screw on type of thing. turn off boiler, turn off all the boiler valves, unscrew the unit, after unplugging it, (otherwise you will get twisted) You will get some water coming out, not a lot, Careful of any seals, give the fitting and the bit that come out a clean, If you have a test meter, check the bit that comes out for continuity, use a magnet to see if the reading changes, if it changes, all ok, refit, done. if no change to continuity when you put a magnet next to it, switch is faulty, and you will need to get a new one, fairly cheap. I did eventually make my own reed switches to go in, using a higher quality reed, But that is a different story.
SD
December 2011
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix home heating systems.