Combi boiler supplying a couple of taps and a lorryload of radiators on
(I think) two circuits (err... that is the radiators are on two
circuits).

Child turns tap on and is scalded by water that seems to me to be well
above 60C (lots of steam etc.)

Fiddling with the "tap temperature" dial is interesting; the first water
you get is scalding, but after a while it settles down to a lower
temperature, related to the setting of the dial.

The boiler has a temperature indicator on the front under the flap; a
row of neons or LEDs or something indicating up to 80C. After running a
tap for a bit, they go down to 40C or 50C, but climb right up to 80C
when the taps are closed.

Now I think this might related to the hot weather; the radiators in zone
1 *all* have thermostatic valves which are obviously, in this weather,
not keen to pass any water. There is no obvious sign of a heat-dump
loop. Zone 2 has a room thermostat which is again, obviously, off
(indicating 25C this evening). The boiler (CH) is controlled by a
timeswitch which no-one has seen fit to turn off, so is calling for
heating, and the function switch on the boiler is also still selected
for both heating and hot water.

Is it possible that because there is a call for CH but nowhere for the
heat to go that it's being dumped into the DHW? The boiler has a
"preheat" function. If so, should we be looking to take the TRV off one
of the radiators, or installing a room thermostat for zone 1? Zone 1,
BTW has one "cold" area (entrance lobby), a corridor and several smaller
rooms which heat up much better.

Or should we be looking at another fault?

I only thought to pose this question here a few minutes ago and so I've
no further details of the boiler (make, size etc.) but if it helps I can
get them very easily. The boiler is likely to have quite an output as it
is running 9 radiators in zone 1 and a further 9 (IIRC) large ones in
zone 2.

Any thoughts appreciated.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... Even a blind pig stumbles across an acorn now and again.