Hi. The last week or two my hot water has not been performing properly. The water only heats up if I turn the taps on at a very low flow rate, so that it takes 15-20 minutes to run a bath instead of the usual 5 minutes.

Baxi 105e Instant combi boiler, 10 years old, only previous problem was a hole in the DHW diaphragm about 18 months ago.

Before discovering the water will heat if I run it slowly enough, I just thought it wasn't heating properly. All I got was lukewarm water, while the lights on the boiler were telling me the hot water was quickly reaching maximum temperature and the burner was shutting down until it cooled a bit and then coming back on. I swapped the DHW and heating temperature sensors but the problem stayed with the hot water.

Is the cause likely to be the plate heat exchanger?
If so, can this be cleaned out or will it need replacing? (Not a hard water area, never any rock in the kettle.)
If not, what is it likely to be?

Any help would be much appreciated.

Thank you for replying.

thescruff wrote on Mar 23^rd, 2013, 11:35pm:


I had a go at flushing the system about 10 years ago before replacing the boiler, but not since. So probably not that clean, although no cold spots on any radiators.

thescruff wrote on Mar 23^rd, 2013, 11:35pm:


Would that be the same chemicals as used for flushing the system?