Arfa Daily wrote:

Thanks all. Ok. Before going on to my other question on these combis, a part
1(a) to this question ...

Talking this through with said daughter tonight, it turns out that she wants
to replace the shower as well. This is a wall recessed 'conventional' mixer
shower with temperature and flow valves, and is over the bath, so presumably
fed from the same pair of pipes as feed the bath taps. I'm going to assume

Well if it was plumbed properly, then the hot supply would have come
from the cylinder in the usual way and could well have shared a pipe
with the hot tap. The cold however ought ot have had a dedicated feed
from the cold tank in the loft (which would have been connected a little
lower down the tank so that the hot water would stop first should the
main tank drain completely). You will need to find if this is the case,
and how it has been replumbed if it was.

that this has been in there since before the boiler was changed. Now, she
says that the pressure is not very good, so I'm wondering now as to what
sort of pressure would you expect from one of these boilers, because I'm
guessing that the pressure must be restricted from that of the rising main,
to allow the bloody thing time to heat the water as it passes through ??

You need to distinguish between pressure and flow rate. Combi boilers
will usually deliver very good hot water pressure (assuming the cold
main does), and this usually results in a good forceful shower. The flow
rates they can deliver (especially the lower power ones often fitted)
can be less impressive when compared to a stored water system here[1].
For most showers this is not a problem unless the one she has required
vast flow rates as well - e.g. like the ones with body jets or big
diameter drencher heads.

[1] if the usual pedants are reading, yes we know this is not always the
case and you can do better etc, but we are talking generalisations here.

As someone else had suggested, I was considering fitting a pair of service
valves to allow the rest of the system to be repowered, but I'm now thinking
that if the pressure really is low, then I'm not going to be doing myself or
her, any favours by dropping it still more with valves in the lines.

At mains pressure this is going to have little impact. If in doubt you
could always use the so called "full bore" service valves - these do not
introduce any restriction.

That aside, are any types of shower valve more suitable than others, for use
with combi boiler hot water systems ? Any specific recommendations ? She is

A thermostatic one is best since the input temperatures can fluctuate
based on the actual demand for water in the house. e.g. a washing
machine deciding to fill while you are in the shower will not only drop
the pressure at the shower - it may also reduce the output temperature
of the combi by increasing the flow rate of the water through it. (note
most combis do not regulate to the flow themselves to control the output
temperature - they will typically regulate the gas rate to prevent a
user preset temperature limit being exceeded - but not the other way round.

not going to be wanting to spend too much, and we are probably going to be
talking B&Q here (yes, I know, but she's only young ...)

Something like one of the Bristain bar mixer type showers can be had for
under £100 in many places. Nothing special, but they will do the job and
are almost disposable at the price.

--
Cheers,

John.

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