shower in loft is cold unless I turn on sink cold tap.

[benathycromalin]

Hello,
I've got a thermostatic shower valve feeding a shower head in the ceiling of my bathroom. The bathroom is in my loft, so 3rd floor. I have a system boiler setup on the ground floor.
The shower was running stone-cold whatever the settings so I fitted a new cartridge but even now at it's hottest setting on the tap the shower is still only just warm (almost cold). The only way to get the shower to be hot is to turn on the cold tap in my basin in the same bathroom. I then get a low-pressure hot shower.
Both the bath and basin hot taps have good pressure and I wouldn't say the cold tap is excessive pressure in comparison.

Can anyone tell me what is happening? It seems like the cold water pressure is so much more than the hot that the balance is off...?

Any help will be most appreciated.

Shower valve is a very old Bathstore 3091 but I found all replacement parts and they fitted fine.
the boiler is pretty new and functioning Worcester and Bosch with old Ariston cylinder.

Thanks in advance
Ben

 

[snowhead]

Turning the Basin tap on is reducing the Cold pressure at the shower, suggesting without it on the cold at the shower is overpowering / crossing over to the hot side.

Has the shower ever worked correctly?
What's the Cold pressure like compared to the Hot elsewhere in the house?

 

[benathycromalin]

Turning the Basin tap on is reducing the Cold pressure at the shower, suggesting without it on the cold at the shower is overpowering / crossing over to the hot side.

Has the shower ever worked correctly?
What's the Cold pressure like compared to the Hot elsewhere in the house?

Thanks for replying.
Yes it has worked correctly. It had got progressively worse as we've been here for 7 years.
One floor lower the cold water pressure is the same as the hot on the same floor, at a push I'd say the hot has slightly more pressure.

 

[benathycromalin]

Thanks for replying.
Yes it has worked correctly. It had got progressively worse as we've been here for 7 years.
One floor lower the cold water pressure is the same as the hot on the same floor, at a push I'd say the hot has slightly more pressure.

"overpowering / crossing over to the hot side." - does that suggest that the main body of the shower valve has a problem rather than the cartridge? Or that the balance of hot/cold water is just so different that this happens? or that the hot water supply to the valve has a restriction?

 

[snowhead]

"overpowering / crossing over to the hot side." - does that suggest that the main body of the shower valve has a problem rather than the cartridge? Or that the balance of hot/cold water is just so different that this happens? or that the hot water supply to the valve has a restriction?

I'd suspect most likely in this order;

that the hot water supply to the valve has a restriction
that the main body of the shower valve has a problem
the balance of hot/cold water

Out of curiosity, with the shower on (running cold) turn on the cold basin tap (then the shower runs hotter?) then turn on the hot basin tap as well, does the shower run cold again.

 

[benathycromalin]

I'd suspect most likely in this order;

that the hot water supply to the valve has a restriction
that the main body of the shower valve has a problem
the balance of hot/cold water

Out of curiosity, with the shower on (running cold) turn on the cold basin tap (then the shower runs hotter?) then turn on the hot basin tap as well, does the shower run cold again.

I did the above.
Shower on (set to full hot) and it runs cold, turned on cold basin tap full, shower runs very hot (medium flow not terrible), turned on hot basin tap full, shower runs cold.
Note: If I turn the cold tap on only 1/4 open it makes the shower run at a good hot temperature.

what sort of restriction could it be if it were that? I have a water softener.

 

[MARTIN STANJER]

Hello,
I've got a thermostatic shower valve feeding a shower head in the ceiling of my bathroom. The bathroom is in my loft, so 3rd floor. I have a system boiler setup on the ground floor.
The shower was running stone-cold whatever the settings so I fitted a new cartridge but even now at it's hottest setting on the tap the shower is still only just warm (almost cold). The only way to get the shower to be hot is to turn on the cold tap in my basin in the same bathroom. I then get a low-pressure hot shower.
Both the bath and basin hot taps have good pressure and I wouldn't say the cold tap is excessive pressure in comparison.

Can anyone tell me what is happening? It seems like the cold water pressure is so much more than the hot that the balance is off...?

Any help will be most appreciated.

Shower valve is a very old Bathstore 3091 but I found all replacement parts and they fitted fine.
the boiler is pretty new and functioning Worcester and Bosch with old Ariston cylinder.

Thanks in advance
Ben

Do you have another shower elsewhere in the house?
If so, and as you say the pressure of both hot and cold appears to be similar when tested at other outlets, it could be that other shower is causing the problem.... the explanation is this: If, like many mixer showers it is designed with the mixing cartridge/chamber upstream of the on/off flow valve, it relies on having check valves fitted to the hot and cold inlets to prevent cross flow. When you draw hot and cold simultaneously from another outlet, as you do when you use the problematic shower, the dynamic pressure in the pipework connected other remote outlets including the other shower drops. As any shower will be demanding typically 80% hot and 20% cold water, the pressure drop in the hot pipe is greater than the cold. If the check valve in hot inlet to the other shower is stuck open or partly open, some cold water can flow into the hot supply line via this shower valve, cooling it to the point it could prevent the problem shower getting hot enough. Hope this makes sense!
I've had to deal with this perplexing problem a few times over the years. The offending check valve may be accessible to service on the shower in question, but if it's tiled in or otherwise not possible to get at, a separate check valve can be fitted to the hot pipe to that shower to resolve the issue.
Hope this might help!