Wife came downstairs at 10 pm last night to tell me that there was no hot water. Checked the combi in the garage (2 yr old Worcester Bosch Greenstar) and found it was flashing 'EA' on the display - and gurgling like mad.
I immediately suspected that the condensate drain had frozen up - and this turned out to be the case. When the boiler was installed there was no available internal drain point for the condensate so the drain pipe had to be run out through the garage wall. A channel was cut across the concrete side path, and the plastic 'soakaway' for the condensate sunk into the ground at the edge of the path.
I insulated and boxed-in the the foot or so of pipe on the outside of the wall of the garage. Insulated the run of pipe under the path before cementing it over. But there was about four inches of uninsulated pipe between the edge of the path and the soak-away. Despite it being about four inches below ground - the extreme low temperatures last night (-17 in this area!) obviously did for it.
A few kettles and pans of hot water got it de-iced and I could fire up the boiler again - but I suspect that quite a few condensing boiler owners have been calling in heating engineers for this problem this winter!
After firing up the boiler I thought it still had a problem because the display began flashing -| |- . I had to download a pdf of the engineers' servicing sheets to learn that this just meant that the 'syphon fill programme' was running - and it wasn't an error code. It took about 20 minutes of the boiler running at minimum to refill the syphon and then all was well. All nice and warm this morning thank goodness. Don't know how easy it would have been to get a heating engineer out this close to Christmas. Doesn't bear thinking about - Christmas with no heating or hot water!