S53 indicates a blockage. Your shower must be putting the boiler under maximum request for HW delivery where your taps are not.
The blockage could be in possibly 4 places:
Either of the hoses (flow or return), if they are not of the new hose type, they are likely to deteriorate internally (these have now been replaced by solid and flexible copper tubes).
In the filter (prior to the DHE) left hand side of the DHE ) could be the rubber from the flow hose causing the blockage).
The DHE itself is blocked, due to being fitted on an older system without the system being properly cleaned.
S53 is basically a 'holding mode' for up to 15 minutes, the boiler suspends delivery as a self protection measure, this is due to the flow and return temperature differences being too great (ie; the water can't get cleanly through the boiler and DHE).
Replace both hoses with new pipes, clean the filter, and if neccesary, clean the DHE, you may need to consider cleaning the system to prevent a re-occurence.
Carefree, March 2011
