Why is hot water taking so long?

I have moved into a house with a Vaillant TurboMax Plus combi boiler, I think it is 6-7 years old.

I have to leave the hot water tap running for at least a minute before the water runs hot, though the hot water outlet pipe from the boiler feels hot within maybe 10 secs of turning on the hot tap. I estimate that the pipe run from boiler to tap is about 11 metres, and by my reckoning (which could be wrong!), that length of 15mm pipe contains about 1.5 litres of water. But, in the minute that the water has to run before it is hot, a good 10 litres must be wasted (estimate).

Note that I've tried enabling the WarmStart function on the boiler, but this has little or no effect on the hot water delay.

Why might it be taking so long for the hot water to come through?

Also, the pressure gauge on the boiler is right at the lower edge of the green zone. Might this be related to the problem above? How do I increase the pressure in the system?

Stephen G
June 2008