How can I replace Halstead fine gold combi boiler's diverter valve ?

Hi cypleung.
A similar thing happened on our Halstead Trio a few years ago - that turned out to be the pressure switch sticking. The key thing was that the boiler was just taking a couple of minutes before firing up. It gave the impression that the heating was OK but DHW was not - initial diagnosis was the diverter, which turned out to be incorrect.
One symptom was that radiators cooled down quite a lot in between warming back up.
One thing to check, leave a DHW tap running for a bit (with the heating off) and see if it fires eventually. Also, you can try tapping the pressure switch and see if that sorts it.
Check that the pin pops up from the diverter when you have DHW flow, and that it engages the microswitch.
Pressure switch and Diverter are both pretty easy to DIY (no gas or flames!). Banico sell diverter values for about £35.
I hope that helps. Good luck.

E
May 2008

Should tell you how to remove and replace in the installation manual

T
April 2008