Shower temperature - too hot to handle!

[Up North]

I have a Mira shower linked to my hot water tank which works well when my boiler thermostat is on the LOW setting. The water temperature is controlled using the rotary dial and I'm able to adjust it to make the shower warmer or cooler as required. Unfortunately when the boiler is set to HIGH (or when bypassing the boiler when it was recently faulty and using the electric immersion heating element) the water is almost at scalding temperature and is completely uncontrollable. Moving the rotary dial to a cooler temperature has absolutely no effect and the water remains at a very high temperature; the shower is effectively unusable as I am unable to reduce the water temperature. Any ideas - is it any easy fix or is it a plumber job? Grateful for any suggestions. Thank you.

 

[Chuck]

Grateful for any suggestions. Thank you.

Your description make me think the cold water feed to the shower is insufficient. This could be a strainer that has clogged, an isolation valve left partially closed, an inverted-U section of pipe containing an air lock, pipe that has been crushed/kinked, etc.

 

[Knappers]

Make sure valve is piped up with cold on right?

 

[cjg]

is it a bar shower, with r.h.side on off, l.h. side mixing?

 

[Up North]

Your description make me think the cold water feed to the shower is insufficient. This could be a strainer that has clogged, an isolation valve left partially closed, an inverted-U section of pipe containing an air lock, pipe that has been crushed/kinked, etc.

Many thanks for your reply; I'm now checking the various suggestions made. Much appreciated.

 

[Up North]

Make sure valve is piped up with cold on right?

Many thanks for your reply; I'm now checking the various suggestions made by respondents. Much appreciated.

 

[spanner]

Probably got boiler running at lowest cycle. Be careful, legionella and waters to be stored @ 60 degrees.t te To be honest no ideas' ??
The immersion back up is probably set the right temperature, as for the blending its like the mixings taking place in the valve body and the hots the better pressure doesn't allow it to blend.
Is the unit a thermal storage??