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leaky problem with universal thermostatic mixer shower?

hello all.
I am having a problem with my power shower which had a sceptre thermostatic mixer shower ( the cylindrical type).
The first one a "sceptre" was fitted by a plumber and worked fine for awhile but started to leak when fully switched off, sometimes the leak could be stopped by turning on/off a few times but would start again.
I bought me another on ebay and as I could see nothing wrong with the cylinder case, just removed the inner brass fitting, clean the inside thoroughly and replace with the fresh brass bit from the new bought one .
Again this worked ok then problem reoccurred. even if power was switched off from motor, it would start with a gush, sometimes accompanied by a (doc-doc-doc) sound from the motor. fortunately the system is fitted with 2 taps for incoming hot/cold and 2 for outgoing h/c but I have to turn these taps off with the aid of a plumbers wrench in order to stop leak completely.
This may have nothing to do with the problem, but with both fittings when having a shower and turning the knob to the coldest, the water was always what I consider to be not scalding but too hot for my taste, and the only way to solve this problem would be to adjust the incoming hot tap (pre pump).
thanks in advance for any advice.
bernard

bernard
July 2011

D.I.Y, Plumbing Mixer Hello Power

I think that I may have found why my mixer leaks.
I removed the brass cartridge today, and I noted that at the rear of the cartridge (this is where an opening is controlled by the large knob that turns on the shower) the bit that shuts off the water by acting a bit like a guillotine, in the fully open position the space is fully open , but when the knob is turned fully clockwise as per shutting off , then the guillotine does not full close.
about a 1 mm opening at best remains, maybe due to bad original fitting together or bad chinese? manufacture
I tried to pull out the rear bit after removing the circlip without result.
the type of cartridge can be seen at (but not bristan)
http://www.ebay.co.uk/itm/Bristan-Thermostatic-Cartridge-cart-5-06732COMPL-/120748987655?pt=UK_Home_Garden_Bathroom_Shower_Units_PP&hash=item1c1d335507
the above has a 3rd rubber ring at the end where mine has not.
my hot water supply is not coming from a tank, but directly from hot water cylinder,

bernard
July 2011

Is there a way to get round that by say adjusting the hot or cold taps on the input side of the pump? and is there any way of testing the pressure for hot and cold? and does the hot/cold setting on the mixer Also make a difference to the pressure differential ?
the cold water is coming from loft tank which is just above the first floor hot water cylinder, which supplies the hot side, the pump and hot water cylinder are in the same cupboard just to give a picture

bernard
July 2011

thanks toptrish
Is there a way to get round that by say adjusting the hot or cold taps on the input side of the pump? and is there any way of testing the pressure for hot and cold? and does the hot/cold setting on the mixer Also make a difference to the pressure differential?
the cold water is coming from loft tank which is just above the first floor hot water cylinder, which supplies the hot side, the pump and hot water cylinder are in the same cupboard just to give a picture.

bernard
July 2011

some showers only allow cold water from the same header tank as the hot water,if its been piped from the mains the pressure differential could be the problem

toptrish
July 2011