Initial thought, flow valve sticking, failing that problem with pcb. As pcb would be expensive, I would look to flow valve first, going to be difficult to test, as by disconnecting it, you change the electronic, I would think that a voltage test of the switch is best. Take a voltage reading from each connection of switch, Boiler on. One side would read higher voltage, when no water flow. so go to the side that gives no/low reading turn on water, reading should then be same as the other side, no flow. turn off water. reading should change. no change faulty switch.
Change, possibly faulty pcb. If it is pcb, If not causing any other problems, as it would be expensive, leave well alone, IF just a problem with indicators.
SD, November 2011
