So which would be the best combination..
Baxi 105e + Mira 415 Combiforce (pressure balanced)
Baxi 105e + Mira Excel (thermostatic)

and why...?

jhiker@hotmail.com wrote:


> So which would be the best combination..
> Baxi 105e + Mira 415 Combiforce (pressure balanced)
> Baxi 105e + Mira Excel (thermostatic)


I would opt for the Excel - but by a small margin in this case ;-)


> and why...?


I am not convinced about the 415, in particular calling it the 
"Combiforce" seems inappropriate - it sounds like a product that would 
be at its best with a mains pressure stored water system or heatbank.

If you have a look at the installation and user guide for the 415 it says:

"The Mira CombiForce 415 is a pressure balanced shower control which 
maintains a constant outlet temperature irrespective of changes in inlet 
pressures as long as the inlet water temperatures remain the same.", 
then later it says "Hot and cold water supply temperatures MUST remain 
relatively constant."

That last bits would seem to be critical. With a combi you can't rely on 
a constant output temperature. You can set its maximum temp with the hot 
water stat if it has one, but the minimum temp is dictated by flow rate.

So for example someone turning on a cold tap may drop the pressure on 
both hot and cold (and hence flow through both), the shower will see a 
reduction in pressure on both inputs and make the assumption that the 
pressure is still balanced. The boiler however will be providing hotter 
water (assuming it was not on the thermostatic limit).

A washing machine doing a hot fill will again drop the pressure on hot 
and cold (since the combi is sourcing its water to heat from the cold 
supply), so equal pressure drop again, however the output temp of the 
boiler may fall if you exceeded the flow rate that it can sustain the 
current temperature at.

In reality the 415 will obviously work better than an uncontrolled 
shower, it will work better with high power combis, and with combis 
where the hot water stat is set to a lowish value (e.g. 45 degrees), and 
better where the property is served by a nice fat incoming supply pipe.

Having said that I have an old Mira non thermostatic and non pressure 
balanced shower on a 35kW combi and it is usable. Adjustment takes a 
little bit of practice. SWMBO however opts to go use the new 
thermostatic shower because it requires less accommodation of quirky 
behaviour!


-- 
Cheers,

John.

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