Anyone familiar with this combi (as subject)? A friend of mine has one and correct operation of the DHW side has become somewhat intermittent.
This boiler uses a purely hydro-mechanical method of operating the diverter valve: a differential pressure sensing thing with a large diaphragm senses flow in the CW feed and actuates a push-pin. The latter moves a pivoted lever, the other end of which operates the 3-port diverter valve. The diverter valve end of the lever should also operate a microswitch which provides a DHW demand signal to the PCB and fires the burner (if not already firing for CH demand).
Fault symptoms initially were no hot water unless the boiler was already firing. The lever was moving enough to operate the diverter (at least partially), but not quite far enough to operate the microswitch. An initial bodge cure was provided by bending the lever of the microswitch a tad. This lasted only a few days; same symptoms returned. I've replaced the microswitch as a precaution, but now find that the travel of the lever is grossly insufficient to operate it, and hot water (when firing for CH) tends to be lukewarm since, presumably, the diverter valve travel is also incomplete.
Clearly there is a problem in the hydraulic/mechanical system. But is the pressure sensor not pushing hard enough or is the diverter valve too stiff. To move the lever far enough by hand to operate the switch seems to need quite a lot of force - but I've no feeling for what is normal here. Is this a is known or common fault? The diaphragm for the pressure seems to be a commonly available spare - is that a clue? Is its replacement a straightforward procedure?
Any thoughts welcomed.