Shower mixer taps

Boilers are inherently dangerous for the average DIY for so many reasons, contact British Gas and have them come back and fix it, tell them it was fine before the "service". They may simply have a control valve shut off.

There should be a hot water limiter behind the knob on the shower - shingle handle, undo the handle and move the adjustment to allow more hot water. Not familiar with mira discovery mixer

The thermostatic mixing spool cartridge may be worn out. The low water pressure may indicate sediment in the cartridge as well. This can be easily removed by hand tools

from a plumber all hot and cold connections on all major showers are hot on the left and cold on the right just like the taps on your sink or washbowl

Hi,

If the hot and cold are fitted the wrong way round then the thermostat on the shower unit cannot operate properly!

Most thermostatic mixer showers have a 'bi-metallic' thermostat, if you supply the hot to the cold and vice versa IT WILL NOT WORK.

It is like wearing the left shoe on the right foot and the right on the left! It doesn't work.

Re-install the hot and cold to the correct supply, and this will sort it.

I hope this helps.

I think some shower valves have a safety setting to prevent burning. maybe you could adjust that to be hotter.

you mixing valve may be going bad,do you have hard water? you may just need too take it apart and clean it

If you are having trouble only at the one fixture (shower), and no where else, the problem is most likely in the shower valve...which either needs new cartridges, or a complete replacement.
hope this helps

Modern shower valves have an "anti scald device" in them to prevent scalding from to hot water.

They come preset at 120 degrees.

Sometimes they can start to malfunction and all you get is warm, not hot water, they can also be intermittent.

This will only effect the shower valve though, not the other faucets.

hi did you run a seperate cold water supply from the storage tank to the shower pump & also a seperate hot supply from the hot water cylinder, it sounds as though the cold water is crossing into the hot service & pushing its way up to the tank as its the only way it can go, sounds as though the cold water connection to the shower is not tank fed & possibly directly off the water main.?