Mixer shower problem

[orbis]

Hi folks,

I wonder if someone can offer any advice.

I've just retiled my bathroom, and needed to remove my mixer shower unit in the process. Having refitted it a few days later, it's behaving totally differently - beforehand there was a nice gradual change in temperature as you changed between hot and cold, with no noticeable change in pressure.

Now it seems to be only doing either hot or cold, with no happy medium.

The pressure also changes - it's difficult to describe but here goes... Starting from cold, you turn the temperature lever a long way and suddenly there is a dramatic increase in pressure and the shower goes (very) hot. If you turn the lever a long way back the other way, the water suddenly goes ice cold and the pressure drops again. Wherever the lever is between these two extremes could produce either hot (high pressure) or cold (low pressure) water from the shower, depending on which 'extreme' you last visited. Clear as mud, I know. It's b*ggered, basically.

Our hot water system's unvented, which I sort of assumed meant that both hot and cold supplies would be working at the same (mains?) pressure. Anyway, the hot/cold shower feed is just teed off the feed to the bath taps, which, er, work fine.

Is it possible there is air trapped in the unit - or dirt/scale build up, in which case should I attempt to completely open the mixer unit up and give it a good clean? Or is something likely to have gone kaput - in which case am I likley to be looking at new parts or a new shower? The only identifiable mark on it is the word "Hydramax".

Cheers.

[BigWallop]

You had to turn the water off at isolator valves, before you worked on the shower. The problem is probably in the cold water isolator valve, not the shower mixer. Make sure both isolator valves are fully open.

[orbis]

If only! Annoyingly there are no isolator valves on the supply to the bath taps (and therefore the shower mixer). I think this may be against the regs, but that's a problem for another day...

I had to completely turn off the water to work on the shower.

[BigWallop]

If the water was off and drained, then has something jammed in the cold water outlet from the water tank? Did you wrap PTFE tape or joint compound around any fitting when re-installing the mixer valve? Is the hot water supplied from a different source than the cold, or are they both supplied from a storage tanks?

The only other thing I can think of, is that you have turned the hot water supply on, more than it was before. Like hot water from a combi-boiler supplied from the mains, and the cold supply from a tank in the loft. The hot water will be reaching the mixer at a higher pressure than the cold water unless a regulator (gate) valve is in the line somewhere. This regulator valve may need resetting.

[orbis]

No cold water tank, sealed hot water cylinder - unvented system. On every other outlet both the hot and cold seem to be working at mains-type pressure. Since there's no pressure difference between hot/cold anywhere else I guess it could be some debris in the mixer itself. Will turn the water off again and investigate.

The only reason I'm wary is that the entrance to the inner sanctum of the mixer unit is via for of those 'star' screws. Which has always said to me 'you don't want to be doing this unless you know what you're doing'. Ah well!

Thanks for your help, BigW.

[Tim Mitchell]

In article , orbis writes

I took my shower mixer to bits, it had torx screws, but inside it was actually very simple, so I wouldn't be too scared. Mine has some mesh filters actually inside the mixer, so it could be you've got something similar with some crud in it.

It certainly sounds like a hot/cold pressure imbalance for whatever reason.