My family's central heating and hot water is supplied by a condensing boiler feeding an unvented system.
When I turn on the cold tap in the kitchen (not mixer taps) after a period of non-use, the water runs cool for a second or two, then it runs hot for three or four seconds before cooling to cold.
Any idea what causes this and what could be done to avoid it?
How hot? Could it simply be that the cold pipe runs alongside a hot pipe somewhere, so that some heat gets transferred to the stationary water in the cold pipe? If so, you need either to re-arrange the pipework or to insert some lagging between the hot and cold pipes.
In message , John Aston writes
hot & cold pipes run too close together
insulation/move the pipes
On Sat, 10 Apr 2004 19:42:07 +0100, in uk.d-i-y "John Aston" strung together this:
I think most combi's do this
I'm not sure why they do it though. It does depend on whether your boiler has an internal store or not and whether it is switched on. If it is using this feature then the cool spot is the transition between the stored water and instantly heated water.
Heat transfer between pipes. Find where the pipes run close to each other and lag at least one of them.
errm - the OP is talking about the cold tap here - what you seem to be describing is what happens when a hot tap is used.
How about the first slug of cool water being what is in the pipe between tap and boiler, then the contents of the heat exchanger which might be hot from heating duty use. Asking for hot water causes the boiler to switch over to its hot water function. Some will actually stop and run up again in this case but those that don't will need to switch up to full gas rate and raise the primary temperature before creating "proper" hot water output. Knowing what combi is involved would be a great help in clarifying whether it is possible to do anything about it short of swapping the hot water system
Here's another one who hasn't read the question!
He's complaining about the COLD water being hot - not about the HOT water being cold!
On Sat, 10 Apr 2004 21:33:16 +0100, in uk.d-i-y John Rumm strung together this:
Oops. I was in a bit of a rush when I wrote that, apologies to all who were misled.
Cold water pipe lying alongside hot water pipe with inedequate insulation between them.
At least it won't freeze in winter.
SNIP
Oops! (Hangs head in shame)
Thanks for the advice.
I'm checking out the pipes now...
Somewhat off topic, I noticed in an earlier thread
I'm doing the same. May I ask what models you used and whether the flow rate drop is causing a problem?
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