Low hot water pressure after fitting thermostatic mixer

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Hi,

I have a 2 storey house with hot water tank on first floor with cws directly above.
I recently fitted a thermostatic mixer on bath situated on ground floor approx 12ft below cws.
The hot flow to normal taps is good but when I turn the bath hot on flow is minimal which is not entirely unexpected.
I think I need a positive head pump like a salamander ct75 to boost pressure just to the mixer which incorporates a shower.
My question is this;

My cold pressure is superb but do I run a new cold feed pipe from cws to pump or just use the already powerful mains cold supply?.
My reasoning is that if the mains supply failed (albeit rarely) then only hot water would be fed to the shower which could be dangerous.
Obviously running this pipe is a pain if i don't need to.
Thanks in advance for any help!!
 
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Ideally both feeds to the shower should come from the same source, in a vented system this will be the cold cistern, with the hot via the cylinder obviously!

12 feet is quite a reasonable head and the water should not need to be pumped unless you're looking for the power shower 'needle-jet' effect.

There certainly should be no need to use a pump to fill the bath. It sounds like you've bought a mixer intended for mains pressure supplies.

I suspect that the easiest way to sort this out would be to put your old bath tap(s) back on, and install a separate shower valve, either a mixer with dedicated feeds, or a venturi shower valve, with which you can use mains pressure cold and hot water from the cylinder.
 
Thanks Mogget.

Just been reading the installation download at salamander website and they say not to connect to mains cold direct as I thought so running a new pipe it is then.

I bought the mixer off ebay second hand from a new build with a combi hence why the hot trickles out.Take your point about being easier to change mixer but the wife likes it so i have to find a work around.
The mixer is staying as its plumbed and siliconed in position.

I am placing the pump in the void underneath the end of the bath mounting onto the floorboards space permitting.
 
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New pipe and pump it is then :)

If you haven't done so already, you might like to post on the electrical forum, they'll be able to tell you about bathroom zones, what can go where, need for RCD protection etc.
 

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