Shower mixer too hot

[John Williamson]

We have a shower which has always been too hot no matter how you adjust the mixer temperature but recently it's really burning hot.

The shower is in a loft conversion and the plumbers teed off a downstairs shower to feed the bathroom upstairs. There are two isolation valves downstairs for hot and cold and when I isolate the hot, there is just a trickle of cold in the shower whilst the sink next to the shower has full cold pressure.

Am I right in thinking the most likely suspect is a faulty shower mixer? I cannot see any visible isolators after the downstairs shower and the fact that the sink has a full flow makes me think it's likely something after this.

Trying to do some detective work to avoid ripping off some very large and expensive tiles

 

[Ben-gee]

Could be a partially blocked inlet filter on the cold, that’s where I’d be looking first.

 

[John Williamson]

Could be a partially blocked inlet filter on the cold, that’s where I’d be looking first.

Thanks a lot Ben. So I did some experimenting (and got a bit wet).

• I removed the thermostatic cartridge after isolating the hot and cold. When cold is turned on it flows freely through the hole where the cartridge was.
• Put the cartridge back in with the hot still isolated, lovely cold water pressure through the shower head
• Turned the hot back on, cold disappears and it's boiling hot no matter what direction you turn the thermostat

Now thinking that I might get away with replacing the cartridge. I've found what looks to be an identical one


Here:
cartridge replacement

Expensive part but cheaper than a new shower and less hassle than ripping tiles off. Think it's worth a punt?

 

[Ben-gee]

First check all the dimensions on yours against the very comprehensive diagram on that page, also count splines etc.

Look inside the brass body and check for scoring/ damage, in particular where the o-rings go.

Clean up the body as best you.

If everything looks ok and the cartridge dimensions match, then yes it’s probably worth trying it.