Mira Extra Mixer tap passing cold water to hot side

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Tyne and Wear
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I have a Mira Extra Bath & Thermostatic Shower Control run from a Combi boiler. I noted that the hot water from the tap was cooler than expected.
I isolated the hot supply thinking to look inside but, on checking that the isolation was complete by opening the tap, I saw (and felt) that cold water was coming from the spout. The cold tap was turned firmly off at the time but cold water was coming from somewhere so I assume that the tap was not seating properly. This is obvioiusly the reason for cooler hot water than expected.

I'm confused because I'd have thought that if the tap wasn't seating correctly it would pass all the time but with hot and cold taps turned off, no water passes to the spout.

Mira suggest a visit from an engineer at £139. I'm hoping that a helpful soul on this forum might point me in a better (and cheaper) direction.

Many thanks
Dave
 
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Thanks for the reply - fitted about 7 years ago I think by a local plumber. I never noticed this before but the bath is only used when we have visitors.
 
In the meantime I've removed and cleaned the cold tap catridge and refitted it with a nice new washer. It has made no difference at all, so I'm guessing that the thermostatic cartridge is somehow the culprit.
 
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Is it £119 fixed price repair ? If it is i would go for it as those cartridges are expensive. Have you checked theres no dirt/solder on the seatings/filters ?
 
Thanks to both for replying. I found a schematic on the web and it's not a proper cartridge as such. It's a so callede "Head Assembly" wich fits on top of a "Sleeve Element" with an "Element" in between. Mira part numbers 122.66 and 122.67, the element being 122.70.

I took the Head assembly out. In doing so it left a chamfered rubber seal and the element behind. I refitted the seal with a little grease to hold it into its housing and put it all together again. Hey Presto, no more cold water from the hot tap!

I'm still wary though. There is nothing substantial; to hold the seal in place. If it works like a tap washer, ie lifting from its seat as the tap handle turns, then I'm guessing it will eventually come adrift again. I'm hoping that it is simply a static seal between the Head and Sleeve Assemblies. I'd be a lot happier if I could sort out how the thing actually operates.

Anyhow, I'm not leaving the old seal in - it's only a temporary fix more to sort out where the problem lay. I've ordered a Seal Kit with lots of bits I don't need incuding, oddly, backnuts to hold the taps onto the bath and I'll have another go when it arrives.

Any other advice would, though, be welcomed.

Thanks again - much appreciated

Dave
 
Only recommendation I would make is, only use silicone grease, don't use mineral/petroleum based, as this will eventually rot the seals. Ah just seen the seal kit and you get a sachet of silicon grease with it. Clean all the old grease out with hot soapy water if it was mineral.

If you're getting the seal kit , then it's a good time to strip it all down and replace them all IMO, though I guess that's what you're going to do anyways.
 
Thanks again for the reply

I shall indeed replace all the seals, though now there's the added expense of a 17mm AF Allen key which I'll probably never use again!
 

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