Swift Flow 80 Combi Boiler Problem

Can anyone help please?
I'm totally in the dark when it comes to central heating systems, so any help would be most grateful.
Swift Flow 80 Combi Boiler with Honeywell control. The problem is that I can only get intermittent hot water supply through the taps, sometimes it comes through hot but most of the time it's cold. However, if I leave the central heating on, or switch it on, the hot water is fine.
The system is approx. 5yrs old. It's never been serviced (to my shame, probably why I've got problems now) I had to replace the fan impeller and motor a couple of years ago.
Water pressure gauge seems ok
Thanks, Richard
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this is the e-mail address for the spares. they have a web site too but cant find it at the moment. rob
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45 + VAT at BES.
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rob
what does BES stand for and have they got a web site ??
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