RE: completely OT, Combi Boiler help/advice

["Phil Harris" <phil@xxxxxxxxxxx>]

>             I have just moved into a house with a combi and
> was sure that there was a problem exactly like you described,
> I have good old British Gas out to check it over. He said
> there was nothing wrong and that the reason you have to
> reduce the flow rate is that by law a Combi can only heat up
> water by a maximum of 35 degrees, so, if as the other reply
> says you have no cold water tank in house then the water will
> come straight from the main supply in the road.
>
> NOW FOR THE Logical bit that made it all fall into place.
> (Thanks to the man in a van)
>
> In the winter the water supply from the street is delivered
> to the combi at around 3 degrees above!!!! In the summer it
> comes in at 13 degrees above. Hence you can fully throttle
> the hot in the summer and still burn your bits, where as in
> the winter you have to throttle it back to keep the water
> toasty and warm.

I don't think that explanation "works"...

If the boiler is only allowed to raise the water temperature by 35deg
then that 35deg would be the same irrespective of flow rate ... The
reason why the water runs hot from a combi and then goes cold if you
draw from the hot supply more rapidly surely has to be simply that the
flow rate requires more heat than the boiler can supply to raise the
temperature of that amount of water in the time that it takes to flow
through the boiler. (i.e. it simply doesn't have the "balls").

It may well be that at a given flow rate a boiler will raise the water
temperature by 35deg and yes, in winter the incoming cold supply is
colder than in summer - I notice this with our electric shower - but I
think it has to be more that the boiler itself is just not capable of
getting enough heat into the water (in terms of sheer BTU's output) than
any legislation.

Phil