Identifying and fixing bypass in concealed shower

9 May 2009
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United Kingdom
I've got a concealed thermostatic shower unit that has started to suffer from cold water not turning off when it's turned off at the wall.
Confirmed its the cold water that is bypassing by turning off the water at the cold water inline isolator and the water stopped leaking from the head.

I've taken the shower unit apart and have in my hand the Flow valve/cartridge ( if that's the right word) and it looks like water has been bypassing an inner washer down by the spindle due to the deposits around the cartridge front. Is this a correct diagnostic? There is a lot of deposit around the rest of the valve,
IMG_20160401_195622.jpg IMG_20160401_202102.jpg IMG_20160401_202942.jpg IMG_20160401_232519.jpg IMG_20160401_232452.jpg IMG_20160401_232446.jpg
So I'm trying to work out if I can take the cartridge apart and replace the seal, after descaling, or its is a replace cartridge job. If it's a replace cartridge job, does anyone know what it is? Its a 22mm spanner to undo the valve, but has no specific markings I can see.

Thanks in advance
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If it's the seal that's leaking, then go down to your local plumbers merchant, and see if the can sell you a replacement. Cleaning it up and resealing it may work, but if it's the thermostat that's gone, then it'll need a new cartridge. This is a suck it and see job.
Thanks, as I thought. It's why I've done it tonight so I can get to the plumbers first thing in the morning and still return after testing for other parts if the valve replacement doesn't fix the problem. ( who works half days Saturdays nowadays!)

I'm desperately hoping it's not the thermostatic cartridge on cost grounds.
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Just had it identified as a trevi therm at the local plumbers merchant. Part ordered.
Cheers for reading!

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