problem with a combi boiler

I've just moved into a new house, and it has a combi boiler. The central heating from it works fine both upstairs and downstairs - all the radiators heat up.
The problem is with the hot water. The hot water tap in the kitchen next to the boiler works fine, but there is no hot water in the bathroom upstairs. The radiator in the bathroom (and other upstairs rooms) work fine, but no hot water comes out of either the shower, or the bathroom sink.
Can anyone give me a few pointers on what the problem might be, where to start looking, etc.
It seems weird that it's only the hotwater upstairs that's not working - if it was all the hot water, or if everything upstairs (i.e. radiators included) that didn't work it would make more sense to me.
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Alastair Rainsbury wrote:

If you mean no water comes out at all, have you checked for a closed stopcock? If however, you get cold water out of the taps, have you checked there is no hot water cylinder or thermal store installed? ... :)
Lee
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Alastair Rainsbury wrote:

Alastair,
Can you hear water flowing through the combi when the upstairs taps run? This is just a basic sanity check to ensure they are actually plumbed in as you'd expect.
If they are, then I'd suspect that the flow control valve on the boiler is set too low. You need to check the manual to know precisely, but on the combi I used to have, it was on the cold inlet to the boiler, and needed just a flat-bladed screwdriver to adjust.
The commissioning guide to combis usually advises adjusting this valve so that turning on a tap to maximum will provide very hot water. However, if the mains pressure changes, this setting can be wrong. I used to just open the flow valve fully, knowing that if I turned on the tap too much, the water would actually be cooler than if the tap were on less.
All of this assumes that your combi is supplied with cold water from the mains. If it is supplied from a cold tank in the loft, then you might not have enough head to trigger the flow switch. Also, even with the mains I suppose the pressure could simply be too upstairs?
Ewan
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Do you have a hot tank ?. If you *do* then it will be treated as a 'heating zone', in which case only the kitchen sink may be on the DHW circuit. If this is the case a 2-way or 3-way valve is stuck preventing the hot tank primary coil from getting any hot water even though the rads (on another heating zone) are working fine.
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Hmmm, that sounds like the best bet so far. I'm now off to start twiddling knobs/valves.
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If all the hot water is produced by the boiler, then it might be that the pipe run (length) is to much for the boiler and you're losing all the heat from the pipes before it reaches the taps upstairs. You might also have a cylinder that stores hot water produced from the heating circuit of the boiler, so check that valves are fully open, and that the heating circuit doesn't have a zone valve (electrically operated valve) fitted to the system and is stopping the hot water cylinder from heating.
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Of course, the previous occupant may have turned off the hot water at the programmer when they moved out.
Christian.
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I've checked that already, the switch points to hot water & central heating
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equipped
go on - tell us!
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Alastair Rainsbury wrote:

I haven't looked at the above site, but if it can't even get the number of US states correct, why should the rest be believed? (There are 50 states, since, IIRC, the 60s.)
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