In message ews.net,
Doctor Drivel writes

Check the pressure vessel charge. This goes flat quickly on these
models. Check the system pressure. It has a low pressure switch, so if
pressure low problems.

If the pressure's stable and, from prior experience, if the pressure
does drop it won't light the DHW either.


I'm not sure if it also has a CH flow switch, if so check this.

Thanks, the CH light flashes continuously, irrespective of whether the
CH/DHW/stat switch etc. are on or off, which seems to imply that there's
an internal fault of some kind before attempting to run the CH.



--
bof at bof dot me dot uk