Mixer shower not working

Hi J Your describing classic symptoms of a faulty thermostatic cartridge on a mixer shower. I would recommend contacting the manufacturer of the shower, using any identifying marks or details from the original installation. The manufacturer will suggest a solution, usually either removing the cartridge and de-scaling it or replacing the cartridge with the appropriate part. If I was attending the job I would also check the boiler was working normally, running a hot tap, bath tap ideally and ensuring the temperature remained constant. Just to rule out any problems with the boiler. Kind regards Lewis Jones

If it's a combi you've got then I'd suggest the flow rate's not enough to kick the boiler in at certain times. Maybe drop in pressure due to high demand or the diverter valve is playing up. You maybe also need to restrict the cold water flow to the shower a little. A lot of them now have little plastic restrictors which fit in the supply inlets. They can be different colors depending on the pressure. It could also be that the hot 1 has some muck floating about in there. You could try removing it & flushing the pipe/cleaning any restriction or perhaps removing it if fitted. Shouldn't really need 1 on the hot unless there's a high flow rate such as from a megaflow. You may be better to have a trained eye check it out though.