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Mira 88 runs hot & cold when shower head raised/lowered

Postby bigzosso » Sun Mar 21, 2010 1:35 pm


The Mira 88 mixer shower we have was fitted when the house was built in 1990. It is cold tank/hot tank supplied. Apart from never having had a strong flow (3.5lt/m!!) it has always worked ok until now.

Last year this problem came and went away, not sure if I cured it or if it righted itself. But now it is back again. With the mixer knob turned to Cold it runs fine. With it turned to Hot it runs fine. When adjusted to "normal" showering temp it is fine, all with the shower head held at waist height. However, lower the showerhead and the water goes cold, raise it above head height and it runs scalding hot! Ouch! You have to lower the showerhead back down to knee height to cool the water flow down again.

It does this with no other taps in the house being used and all the taps have a good water pressure/feed. I have tried "sealing" the showerhead end with it held low and then raising it held high and down again many times, also done this with it set at hot, cold and "normal" temps in the thought of it being an airlock somewhere and trying to force the water back up the line forcing the air out if there is any.

It still runs hot when held high and cold when held low :-(

Any help will be gratefully received. Thanks
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Simply Build It

Postby plumbbob » Fri Mar 26, 2010 6:21 pm

The old Mira 88 was a non thermostatic mixer valve which explains why you can end up having varying temperatures without altering the valve controls. It also only works on low pressure systems.

Exactly why this changes when the head is raised or lowered is somewhat a mystery especially when you say it has worked satisfactorily in the past. The fault cause is really obscure and a solution is not obvious without further information. I can't see an airlock causing the problem.

Is there an obvious difference in the flow rates between the high and low shower head heights? What about when the valve is set to full hot and full cold. Do the rates vary then?

One possibility is the cold feed pipe is partly blocked and the water flow is restricted. As the head is raised and lowered, the hot flow falls and rises because of the change in head of water.

Check the header tank for debris. Make sure the isolator valve is fully open. I don't remember any filters being fitted with this model because that could cause the problem.
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