Unable to control temperature of Shower tap.

[mediter]

I had a new shower room fit on the ground floor some years ago. The cold is direct main, hence very good pressure and the hot through the tank upstairs with adequate pressure. There is also a sink, both single lever mixers (pic of shower tap attached). All was well for a few weeks but then, only the shower mixer, it became impossible to get the right temperature of the water. This is what happens to try to explain...

Let's say the lever is centre down at 30 mins (as if minute hand). The water is cold... so move it to 35 still cold... move it to 40, now scortching hot... ok, so now move it to 35, still hot... go back to 30 still hot... oh dear move it to 25 still same hot. Ok go to 24... ooops the cold kicks in and now it is only cold.... after five minutes of going left to right and right to left in mm, I manage to find the spot at 30 for example, where I started. Now if you dare try to change the volume of the water that will cause havoc again and have to start all over again.

I have no issue at all with the sink mixer, both taps are of the same company and batch. I must also let you know that at some point the mixer was replaced after a year with an identical one but the second one did the same thing. Worked fine for the first few weeks then the above happened.

Any idea were to look for the problem? It looks like the cold water kicks in heavily overpowering the hot or completely shuts down. I can just move the lever by a fraction of a mm and from very hot get only cold or vice versa.

Your advice much appreciated.

 

[terryplumb]

a few points to clarify...you stated that "scalding hot " water can be got at a certain point. that indicates a problem with the temperature of the stored hot water. it should not be delivered to the shower valve at a scalding temp. do you have gravity fed hot water ? if so the cold should not be from the mains,the shower valve needs equal pressure hot and cold to function properly.

 

[mediter]

When I say scalding hot, I wanted to mean it is top hot as per tank temperature. And yes it is gravity so I think the pressure from the main and the hot is too vast to control it. But then I ask why do I not have the same problem in the sink tap? The hot is garvity and the cold is mains.

 

[terryplumb]

I assumed the shower mixer is a thermostatic mixer valve ,which is a lot more complicated than a basin mixer,and should maintain a consistent temperature at the shower head once you choose your preferred temp and flow. it does this within the valve body.

 

[mediter]

I see, so that answers the problem. The solution is installing a pump on the hot water side I assume.

 

[terryplumb]

sorry I may be misleading you. just looked at your pic and it may not be thermostatic. can you confirm it is actually a thermo or just a basic mixer valve please.

 

[mediter]

To my knowledge there is nothing to control the temperature within the tap. It's just a basic one.

 

[terryplumb]

if it is a basic mixer ,you still need balanced hot and cold supply's.some of these are only suitable for high pressure hot and cold. we don't know exactly what yours is . but it will be affected by other things in the property being used whilst showering ,like other taps /toilet/ washing machines etc. if the temperature of the stored hot water is too high you are fighting on all fronts trying to balance cold from the mins against excessive hot gravity fed,possibly with a mixer valve not even designed for the application. my advice would be to correct the plumbing to the valve, by taking a dedicated cold supply from the cold water cistern ( assuming its in the loft) to the cold inlet of the mixer ,this is how it should be done. if the temp of stored hot water is over 60 degrees c that should be sorted. if you still can not get reasonble results from shower ,fit a thermostatic mixer suitable for gravity feeds. regards terry.