John Stumbles wrote:
On Sun, 18 Feb 2007 13:58:15 +0000, Joe wrote:

It's about two years old, non-condensing, and recently is taking a
long time to come up with hot water. It fires up about five or six
seconds after opening the tap, then it's anything up to about five
minutes before the water gets warm, not counting the time it takes
to get to the tap. The more recently it has been used, the less
time it takes. It doesn't seem to depend on the water flow rate.
The red light is on the whole time, but it's difficult to tell from
the sound how much gas it's burning. The CH pipes stay cold.

Is the water coming out at a dribble that's taking a long time to get
through the pipework? In that case it's likely to be scaled up (if you're
in a hard water area).

No, sorry, it's running as fast as it did a month or two ago, when the
problem wasn't there. I expect a slightly slower warm-up in winter, when
the incoming water is colder, but this is excessive. As I say, if I use
hot water again within half an hour, there's no problem, and the flow
rate hasn't changed. It's almost as if there's a huge heatsink that has
to warm up before the water gets any heat.

The non-condensing 24/28i Juniors have combined heat exchangers rather
than separate plate heat exchangers and diverter valves so if the boiler
is firing up straight away it must be heating DHW straight away: you
should be able to feel the DHW pipework inside and just outside the boiler
getting hot and follow the pipework getting hot.

Not obviously. I did wonder where all the heat was going, and I must
assume the burner is throttled back to minimum during the waiting period.