sm_jamieson wrote:
Robert Laws wrote:


...To solve this one needs a thermostatic shower mixer that controls the
cold supply, not the hot.....

Are there any thermostatic mixers that control only the cold flow?


If you have a combi that tries to maintain a constant temp output then
this cycling will not be a problem. But in my previous house this did
happen to some extent. The combi only had 2 settings at 30% and max.
Note: you could still have the problem with a cold control thermostatic
mixer depending on plumbing. If the mixer turned up the cold, this
could rob the combi input, thus less water goes through it and it gets
hotter etc. Not as likely but just about possible.
As far as what the mixer controls, this information does not seem
forthcoming. You would have to examine the internals to see what it
does.
Simon.

That's a good point about the drawing of cold also affecting the supply
of water to the boiler.

I'll have to check my boiler to see whether it does any kind of
continuous adjustment of teh flames or whether is just oges on/off.

it might be better for me to not have a thermostatic mixer at all:
Simply use the hot tap flow rate to control the temperature, assuming I
can get it cold enough that way, but then the shower temp would
fluctuate depening on othehr taps i n the hosue being used. but at
least it would not go into unstable oscillations from icy to boiling!

R