The answer to this depends on what kind of boiler you have,,, Combination or system (heat only )
Do you have a cylinder for water ??
Ste
March 2011
there is a diverter valve somewhere that changes over depending on demand.The way it is controlled will depend on makes and models which you failed to give any info!
A1
March 2011
I can answer this question...
central heating comes on then the hot water is turned on?
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix plumbing.