worcester combi boiler 28i water running cold?

had a worcester combi 28i for about 4 years and am having some problems, heating seems ok but when run a bath water runs cold after about 5 minutes and pilot is out, comes back on after about 5 minutes, reset button does not pop up, had an engineer out who did a service but problem seems to continue, is this a typical problem, is there a typical solution ?? welcome some feedback or advice.