dear AlanE and Onetap,
many thanks for showing interest in my problem.
the pump receives its power via a time-delay switch (to keep the circulator going for a period after the burner has gone off). when the pump had turned itself off after a normal start, the switch was still relaying power - we tested.
after posting here, i have spoken to grundfos technical help. the gentleman says that if the pump is receiving power, at least one or some of the LEDs on the pump's control panel should light up, even if the pump is not turning for some fault. the control panel is designed to show a red LED for fault, green for OK and a line of yellow leds to show the level at whcih the pump is to perform. all LEDs going off, he says, can only mean that there is no power input. i therefore set off looking for faulty electrical connection.
on the pump-end of the power cable, the electrical connections with the input socket were good and wired correctly. this plugs into the control box of the pump. there is nothing really to see inside the control box except that the pins making contact with the socket are soldered directly into a PCB.
i can think of two things not tested. 1) the integrity of the cable between the power relay switch and the pump and 2) voltage of the power relayed from the switch. it is got to be exceedingly unlikely for the problem to beineither of those areas.
i am not sure what is mean by shaft being vertical
. the pipe work is vertical and i thought that might mean that the shaft can only be horizontal - am i wrong?
many thanks once again
