any plumbers on here? Having shower issues

[ik9000]

Any plumbers on here? I'm wondering what might be causing my shower not to go properly cold. It's puzzling me as I can't see anything obviously wrong.

I have a shower powered by a pump unit under the bath that goes to a Grohe mixer unit with a thermostat and from there out to the shower/bath depening on which outlet you choose.

I cannot get the thing cold. I've just adjusted the thermostat which was previously set wrong so the stop now sits at 38C as it should but the coldest setting still doesn't go any colder than before.

The hottest it goes is 46-47C the coldest it goes is 24C. Even if I take the stop out completely and turn the valve all the way it still sits at 23.5C.

The temp out of the adjacent sink cold tap is 12.5C.

If I turn the pump off and run the shower the lowest temp is still 24C but the pressure is just much lower. It suggests that the temp issue is probably not due to pump pressure?

Bathroom sink tap flow rate 11 litres / min.

With the pump off the bath flow rate is only 5 litres / min out of the bath tap.

The mixer unit is at roughly the same height as the sink, and the bath tap much lower down so I would have expected similar pressures, unless the pump is adding resistance in its off-state.

I've checked the hoses and feeds and all the isolators are set to fully-open.

Is this normal? Does anyone know what might be causing this and what I could do to adjust it? I'd like to be able to have a cold shower in summer!

[Kumagoro]

Not a plumber I just like taking things apart.

I wonder if one side of the pump has stopped working though I would have expected the hot side to fail based on the pumps I have had. You could try switching the pipes over and see if it then goes the other way and is then cooler rather than hotter.

[DanceswithUnix]

The thermostatic mixers do fail, I had mine replaced a couple of years ago as it was playing up much like that.

If it dies again, I'm getting another Aqua Lisa Quartz put in.

[Saracen999]

Hard wzter area? Something getting caked up?

PS. Not a plumber.

[oldboy47]

Also not a plumber but in our hard water area I have had to replace 4 thermostat cartridges in 15 years (over 3 individual showers) all in frequent use. The stat would usually cease operating over one of the two flows. The manufacturer recommends descaling in a mix of white wine vinegar and warm water - leave to soak for 30 mins - periodically. For us that would be about every 2 months. Trouble is we forget to do it and then it is too late. I also found that the inner seals in one cartridge had broken over time removing any control.
You may be able to check for advice with Grohe customer support

[ik9000]

Also not a plumber but in our hard water area I have had to replace 4 thermostat cartridges in 15 years (over 3 individual showers) all in frequent use. The stat would usually cease operating over one of the two flows. The manufacturer recommends descaling in a mix of white wine vinegar and warm water - leave to soak for 30 mins - periodically. For us that would be about every 2 months. Trouble is we forget to do it and then it is too late. I also found that the inner seals in one cartridge had broken over time removing any control.
You may be able to check for advice with Grohe customer support

thanks, will give that a shot.

[jimborae]

Also not a plumber but in our hard water area I have had to replace 4 thermostat cartridges in 15 years (over 3 individual showers) all in frequent use. The stat would usually cease operating over one of the two flows. The manufacturer recommends descaling in a mix of white wine vinegar and warm water - leave to soak for 30 mins - periodically. For us that would be about every 2 months. Trouble is we forget to do it and then it is too late. I also found that the inner seals in one cartridge had broken over time removing any control.
You may be able to check for advice with Grohe customer support

What he said, same issue and maybe same manufacture iirc.