Lukewarm bathwater

15 Apr 2018
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United Kingdom

Recently I have noticed that my bathwater is only lukewarm. For the rest of the flat i.e. kitchen tap and the bathroom sink tap the water is warm.

I read the following article and it made me think maybe the faucet is calcified as the flat has now been in use for 10 years and here in London the water is hard.

So I was thinking I should disassemble the bathroom faucet and clean it to see if that makes a difference.

The problem I have is twofold
1) whether I have correctly diagnosed what is wrong.
2) knowing how to dismantle it. I have cleaned all three tap aerators today and found all to have some grit especially the bathroom sink tap so I think that will help a little but I am hoping to dismantle the faucet, clear out some grit in the bath faucet and get everything working fine again.

I have enclosed a photo to help explain my problem.

Also out of curiosity what is the purpose of the button on the right hand side?

All help is much appreciated.


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Press the button and see if you can achieve a higher temperature.
Normally the safety button is set to prevent the hot water exceeding around 40 Centigrade without activating, however wear and age within the thermostatic cartridge might mean the temperature is somewhat lower than should be.
What setup do you have for heating the water? The incoming hot water to the tap needs to be perhaps 10 degrees higher (for correct operation) so if a combi boiler ensure the setting is sufficiently high.
Of course the cartridge could be failing, or the other taps aren't particularly hot either etc
I have pressed the button but it made no difference.
In answer to your query - I have a range tribune cylinder.
How do I open the faucet to get at the thermostatic cartridge? I am wondering if it requires turning the water off,unscrewing the two bolt parts and using a hex key on the underside where the shower cable connects with the faucet.
1. Its not just pressing the button, its pressing the button and turning the control hotter.
2. You have an unvented hot water system. This will normally supply hot water at mains pressure to all outlets. This points to the problem being with the shower.
3. If you know the make and model of the shower try and get the installation instructions off the internet, unless you have the original instructions. Then follow the instructions to reset the normal maximum temperature (as determined by the control being set to its highest value without pressing in the button) to 38 degrees.
4. To remove the cartridge for cleaning you need to:
4a. Turn off the water at the main stopcock. Run off any water remaining in the pipes via downstairs taps.
4b. Pop the decorative caps off the flat end of the temperature control. Remove the screw underneath and remove the control knob.
4c. If there are any splines and stops, these are used to set the maximum temperature. Make a note of / mark there positions.
4d. Unscrew the thermostatic cartridge. Leave to soak in white vinegar or something like Kilrock.
4e. Wash the cartridge and screw it back in.
4f. Reset any maximum temperature settings.
4g. Turn the water back on and test.

I think its unlikely that limescale is the cause of the problem, and more likely that the cartridge has become faulty, or as suggested above, was not set properly in the first place.
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If it's a reasonably new build house there might be a blending valve fitted under the bath.
Thanks oldbuffer for the advice. I have pressed the button and turned the control but it made little difference.

I also unscrewed the faucet and found some more signs of calcification but it made little difference overall.

I believe the model is a
'Hansgrohe - ecostat 1001 sl exposed thermostatic bath shower mixer'. However I am struggling to find online instructions for it.

Also I'm afraid I do not understand your comment

'4b. Pop the decorative caps off the flat end of the temperature control. Remove the screw underneath and remove the control knob.'

How do I pop the cap off the right hand side where the temperature control is? I can not see anything that will easily pop off.

Crezzer - the property is 11 years old. I don't think it has an underbath thermostatic valve.


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1. Have a look at Shows how to get the end caps off.

2. Crezzer could well be right. Look as if your taps are on the long side of your bath. Try looking under the bath with a mirror or photographing with a 'phone to see if there is a TMV closer to the taps. They are meant to be fitted close to the outlet. You can look up "TMV" on the internet to get a picture of what it would look like.
Oldbuffer - I got the cap off, undid the screw in the middle within but could not find a way to take out the cartridge as there is no screw underneath.

I've enclosed three photos to better explain what I mean.


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Should unscrew with a spanner on the flats of the hexagon. Usually normal (right hand) threads, but possibly left handed. Try normal undoing first (while supporting tap body) and if no movement, try and see if left hand thread.
I managed to get to the cartridge and soak it for about 45mins in white vinegar.

I put it back in again and have tested it but there does not seem to be any discernable difference and so the water is still luke warm.

I've enclosed a photo of the cartridge in case that helps.


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For the rest of the flat i.e. kitchen tap and the bathroom sink tap the water is warm.

Warm or can you get them to "Hot"?

If they are only warm then you may be getting crossover from the cold supply into the hot supply and this could be down to the same problematic bath mixer.

Put the mixer back on and shut off the hot supply from your tribune cylinder, or cold supply to it... Whichever you have.
Then open a HOT ONLY tap and see if you get a steady stream of water... This will tell you if cold feed is crossing over to the hot supplies.
Beat me to it :)

You originally described the kitchen tap as "kitchen tap and the bathroom sink tap the water is warm".

Do you really mean just warm ie. not much more than hand hot or scalding as in closer to 60 degrees (the temperature the water in the cylinder should be heated to).

If the water really is being correctly heated to 60 degrees or so then I would run water from the hot outlet on the wall (with the mixer tap off) and confirm you're actually getting hot water to the fitting (another faulty mixer tap could cause cold water to be blended into the hot pipework).

If so then you'll need to replace the cartridge as the wax element within it has failed.
Quick update

I figured it was probably the cartridge as I had hot water elsewhere. I took it out, took a photo and sent it off to the manufacturer (Hansgrohe)to confirm the name of the part. Them and di vapor spare parts website said the same part number but di vapor were £25 cheaper.
Received it the other day, installed it and now have hot water.

Big thanks to everyone here and especially oldbuffer for your detailed advice.

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