SHOWER WITH A MIND OF IT'S OWN! All aspects of plumbing questions and answers, help, tips and information

[onejontwo]

Help please with a mixer shower that doesn't seem to respond to water demands, we've had the boiler checked and been told the boiler is fine. In more detail what happens is that if you take a shower and it's too hot, if you turn the mixer lever slightly to the left it goes freezing and then if you push the lever back it goes red hot! There seems to be no in between ie. warm and luke warm. The shower has always delivered at the temp where the lever is at but now it seems to be either very hot or very cold. But to confuse matters even more some days it seems to work ok. The shower was already installed when we moved in so it must be 10 years old or so and there 's no indication of the make etc. Some one suggested the thermostat on the shower??? Hope you can help, thanks in anticipation.

[plumbbob]

This is the exact symptom of reversed input supplies. In fact, it is the only cause I know of that has this effect.

If the thermostat senses the water is too warm, it alters to add more cold. Because the supplies are reversed it instead adds more hot, which makes the thermostat respond by adding even more hot until eventually the temperature runs away to maximum. The same happens with the cold direction too.

If the shower is turned on and by chance the temperature happens to be exactly balanced, the thermostat won't alter the flows so the shower will occasionally work correctly.

Has any plumbing anywhere been changed that might explain this? I would examine the pipe work carefully!

[onejontwo]

This is the exact symptom of reversed input supplies. In fact, it is the only cause I know of that has this effect.

If the thermostat senses the water is too warm, it alters to add more cold. Because the supplies are reversed it instead adds more hot, which makes the thermostat respond by adding even more hot until eventually the temperature runs away to maximum. The same happens with the cold direction too.

If the shower is turned on and by chance the temperature happens to be exactly balanced, the thermostat won't alter the flows so the shower will occasionally work correctly.

Has any plumbing anywhere been changed that might explain this? I would examine the pipe work carefully!

Thanks for the reply plumbob,
In answer to your question there hasn't been any plumbing work carried out for years (apart from the two bath taps I replaced about 18 months ago) so I see what you are getting at but it seems to be a fault that has gradually got worse over time (within the last few months) which seems to me to indicate something worn , rather than a faulty installation (but hey I'm no expert) Is there some kind of thermostat fitted which can wear/clog up etc?

[plumbbob]

Many showers have in-line strainer filters that can become clogged but that normally shows as poor flow or as simply too cold or too hot.

The most obvious conclusion would be a failed thermostat cartridge though.