Bath/Shower mixer problem

[MB_s]

Hopefully some can assist with my problem.

I recently fitted a new bathroom and, installed a new bath/shower mixer (1/4 turn)
on the bath.

The hot water is gravity fed from the hot water tank.
The cold supply is mains fed.
(Previous bathroom had separate taps)

When using in normal bath mode, the hot water pressure is lower than the cold (as expected)
but is a acceptable and is a useable mix.

However, when switching to shower mode, the hot water just trickles out, and it is impossible to get a good mix and totally unusable.

Last night, my daughter left it shower mode when filling the bath by mistake. The result was the back pressure filled my cold water tank and overflowed out of the side of my house !

I can understand the greater difference in pressure could cause this, but why only in shower mode, and not bath mode ?

Does it sound like the mixer tap unit is faulty?

thanks in advance

 

[ChrisR]

NO, you have a standard set of mistakes. The wrong tap, installed wrongly (illegally in fact) on unbalanced supplies which will never work properly in a mixer.
If you put the necessary non return valve in the hot supply it'll kill its flow even more.

Replumb the cold supply from the tank in the loft.

 

[MB_s]

thanks ChrisR for your help and for the confirmation that there is nothing wrong with the mixer tap set that I brought. (ie its not faulty)

However, could you just clarify what you meant by the wrong tap ?
Do you mean the 1/4 turn type is wrong ? Should I re-plumb to the cold supply and change for normal turn mixer taps t

 

[ChrisR]

SHort answer - replumb first and see how it goes. If the flow is ok then keep it. Should be ok if your hot is ok.
Down the line you might end up with a pump nonetheless. Read around a bit.

 

[MB_s]

Many thanks ChrisR

 

[bobdabuilda]

Is there any alternative to a replumb like a pressure reducing valve onto the cold supply to the telephone shower or an impeller pump on the hot supply?

 

[bobdabuilda]

Hopefully some can assist with my problem.



I can understand the greater difference in pressure could cause this, but why only in shower mode, and not bath mode ?

Does it sound like the mixer tap unit is faulty?

thanks in advance

It happens in shower mode because the hot/cold supplies mix directly within the chamber of the tap unit whereas in bath mode the hot/cold outlets are separate.