I went over there to have a look, and she is dead right. The downstairs
> water is blisteringly hot, the bathroom water - shower, bath tap and basin
> tap - is best described as feebly warm. Given that there only appears to
> be one hot water outlet from the boiler, which presumably splits somewhere
> under the kitchen worktop into downstairs and upstairs feeds, what on
> earth could be causing this odd symptom ?
>
has anyone fitted a thermostatic temp limiter on the bath room? You can buy units that ensure the temp never exceeds a safe 43C and it may have gone duff or someone may have adjusted it in error. This is an example of what to look for
Not necessarily. I'd check the flow rate at the various taps. Is the kitchen tap drawing at a significantly lower rate than the bath tap? If so, does reducing the flow rate at the bath tap (and waiting up to a minute while the water in the pipes is changed) increase the temperature?
Thanks for the suggestion Dennis. I don't recall seeing any such when we did the bathroom refit a few months ago, but then I wasn't really looking. I guess it could also be downstairs where the up / down 'split' takes place. I'll have a look when I go round there next. Probably be the weekend now.
That was my first thought too John, but I turned both the basin and bath taps down to perhaps a quarter of fully on, and left them running, in turn, for perhaps 2 minutes each. There did seem to be a slight improvement in temp, but not as much as I might have expected. Just to make sure that I've got the operating principle right. These combi boilers heat the water 'on-the-fly', right ? A heat exchanger with cold water in and a bloody great fan-blown flame up its chuff to give hot water out the other end, yes ? Some already-hot water 'stolen' from the CH via a diverter valve and a secondary heat exchanger comes into it somewhere ? So basically the gas equivalent of an electric 'on-demand' shower ?
I see from the manual that there is a season correction valve built into this boiler. As I understand it, this alters the flow rate through the heat exchanger, to compensate for differences in the temperature of the incoming water. Given that we have had a couple of weeks now of pretty cold weather, when I first thought about this problem, it occured to me that something might have gone wrong with this system (or the setting of it), and that the (very cold) incoming water was passing through the exchanger at full chat, so not having time to get heated properly, but again, if that were the case, it seems to me that both down and upstairs water would be equally affected, and that the 'reduce the flow' test from turning the taps down, would have resulted in a significant increase in the water temp.
Not that any of that seems relevant to the problem, as the hot water in the kitchen is fine. Just that I like to at least have a working understanding of the system that I am dealing with.
Yes. If you set the bath tap for the same flow rate (time to fill a given-sized container) as the kitchen tap, is the water the same temperature?
If not, what's happening? Is the bath tap a mixer with one knob that's somehow not allowing full hot through (or as dennis suggested, a thermostatic mixer)?
If you're sure the bath tap is only passing water from the DHW supply (i.e. from the boiler) then what's happening at the boiler? Can you see the flames? Is it burning less fiercely when supplying the bath tap than the kit sink one at the same flow rates? (You can tell by measuring how fast the meter's clocking up gas usage.)
If the boiler's running at a lower gas rate for the bath tap than the sink then I'm stumped for now, but at least you know it's something telling the boiler not to work so hard in this case. Maybe this season correction valve gizmo you refer to? (I've not come across thos before, but the only place I've seen Alphas is in a scrap yard :-))
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