Bath mixer issue

[Tom1977]

Hi

I have a new bath shower mixer. When using the shower it clicks back to running as a bath.

Is this pressure fed and is this causing this.? Or is the unit faulty?

Cold water tank in loft feeding
Hot water cylinder first floor
Bathroom ground floor

Is there something I'm missing here?
Can I fix it? Or is a plumber required

Thanks

 

[terryplumb]

Insufficient pressure is most likely,is the cold water also from the loft tank ?
Is it a thermostatic mixer?

 

[Tom1977]

I presumed the cold came from outside straight into house.
The loft has a biggish black tank and a smaller one next to it.
The bath taps are just normal with the shower feed coming off that

 

[terryplumb]

Turn the cold water mains stopcock off ,and see if bath cold tap still runs,if it does it's from the tank.

 

[Tom1977]

Oh. I've done that. Definitely stops when stop cock is off

 

[terryplumb]

Ok cold from mains and hot is gravity. If you set bath mixer to shower but fully cold only ,does the diverter still drop ?

 

[Tom1977]

No it stays on

 

[terryplumb]

Then you have insufficient pressure on the hot as mostly hot used when showering with a little bit of cold mixed in to desired temperature mix.
What tap / shower was previously fitted ?

 

[Tom1977]

It was an electric shower with single cold water feed.


Is there a fix for hot pressure?

 

[terryplumb]

Fitting a pump to hot water supply to bath mixer ,or find a mixer that is suitable for low pressure. What connects hot pipework to bath tap ,22mm pipe,any isolator, flexible hoses etc ?

 

[Tom1977]

It's 15mm, it has an isolator on pipe work and goes on to a flexi into tap

 

[Tom1977]

Or could a thermostatic tap work?

 

[terryplumb]

Or could a thermostatic tap work?

They need hot and cold at equal pressures,so that's a no with current set up.

It's 15mm, it has an isolator on pipe work and goes on to a flexi into tap

Everything there is going against you and reduces flow rate. Gravity hot water would usually be 22mm pipe direct to bath tap,any isolator should be full bore. Flexible hoses have small bore tubing internally and reduce flow rate considerably. All those are ok on mains pressure cold though.
If you run hot water only ,on full, through shower head ,and into a bucket for 1 timed minute ,then measure how many litres are in the bucket that will tell you the flow rate. I.E. 5 litres per minute for example. Tell us what you get.

 

[Tom1977]

Took about 12 seconds to fill a litre from the hot

 

[terryplumb]

That's around 5 litres per minute, which isn't a lot. You need a pump. Altering the things I mentioned would improve the flow rate, but not the pressure. Its debatable if the improved flow would cure the issue ,I am inclined to think it wouldn't, but a pump would.