Are these shower mixers any good with a combi boiler and do they give
the pressure thats claimed.
Also what benefit does the thermostatic mixers give you apart from the
Basically I'm trying to decide between the CDX h2o £79a nd something
like the MIRA 415EV at £236
My mother now has a Mira 415 and a cheap 99 quid shower. She prefers the
latter because it has separate temperature and flow controls. The Mira has a
single dial that was not able to control flow rate and "forgot" the
temperature last used as you have to spin the dial to turn it off, losing
They're off an unvented cylinder rather than a combi, though.
If you are after something relatively inexpensive (Triton Aire for £66
all in) have a look here:
I'd be interested in anyone's opinions of these as I'm thinking of
They're not what you want with a combi: basically they use the pressure of
the mains cold water to boost the flow of hot water from a gravity fed
system to give a reasonable pressure and flow to the shower, but a combi
gives mains pressure hot water anyway so all you need for that is a mixer
 usually: you may exceptionally have a combi whose cold water inlet is
fed from a tank in the roof, giving low pressure.
You want more benefit? :-)
As Christian says, if you have a 2-knob thermostatic mixer you not only get
a shower that stays the same temperature even when someone uses other hot or
cold taps in the house, but you can also start it up and have it come out at
a the same temperature it was last set at without fiddling about. Just don't
share it with someone who likes cold showers :-)
I've fitted the Sol shower valve from BES (£100 inc VAT) to a system with a
Combi and it does what it says on the tin. There's also a 2-knob
thermostatic mixer including shower hose, head and rail etc (all a bit
plastickey) from Screwfix for about £70.
I've got nothing against racists
- I just wouldn't want my daughter to marry one
There should be two mechanisms for temperature control. The thermostatic
control will gradually fix any temperature variation. There should also be a
pressure balancing valve, which is much faster. When a tap downstairs is
turned on, the valve senses the pressure change and chokes off the opposite
supply. This happens very quickly, about 0.25 seconds on mine. It is quick
enough so that it doesn't scaled/freeze you, although you can tell it has
I suppose with a combi, there might be other effects, as the temperature of
the hot water may drop if someone opens a hot tap. However, I'd expect it to
be gradual enough for the thermostatic side of the valve to operate.
Perhaps your valve doesn't have a pressure balancing section, or it has
No, it doesn't have anything like that, I had it in bits recently and it
just has a bimetallic curly coil to adjust the temperature (cheap
When I replace the shower (cos even the thermostatic bit does not work
properly) I will look out for that feature as well. What model of shower
are you referring to?
The one I fitted didn't do that. I tested it by running it at a comfortable
temperature with my elbow under it and turning on the basin hot tap: the
flow reduced quite promtly but there wasn't a long surge of cold while it
settled. This was with the Sol valve from BES, which seems to me to be a
nicely made bit of kit. The HW source was a combi (Ravenheat RSF84).
ISTR I checked the Screwfix £70 job when I fitted that and found it to be
quite stable. That was with gravity HW (with a good head - the bathroom was
on the 1st floor of a 3 storey house) with mains cold.
Things don't like being anthropomorphised.
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