Can't get hot water stable on shower

Hi there, In my opinion your problem is due to unbalanced pressure on the hot & cold supplies to the shower.The mains cold supply is dominating the hot supply They need to be equal for the shower mixer to work correctly. If the shower is tank fed, both supplies need to come from the tank. If it's out of the question to install new pipe work from the loft to the shower valve, installing a pressure reducing valve just on the cold supply to the shower maybe an alternatIve. Hope this helps Mike

the best option fit a thermostatic shower mixer.

need to run a supply from the cold water tank to the cold tap preferably in 22mm this will give you equal pressure to both hot and cold taps

The pressure needs to be equal or the cold will overpower the hot, it sounds like you have down service hot and mains cold.... this will never work unless you equalise the pressure with a pressure reducing valve or run a cold from the tank.

It sounds like the hot water is fed via a tank/cylinder and the cold is fed from the cold water main. If this is the case, then the best course of action is to remove the cold feed from the tap and re-feed it from the same cold water tank where the hot water cylinder is fed from. This will ensure the hot and cold sides of the mixer tap receive the same pressure and flow rate of hot and cold water. You could also place a twin impeller pump inline with the mixer tap to give you a much better flow rate, but again the mains cold water feed needs to go and be tank fed. If you need the work carrying out, why not post a job and get some quotes - most of us offer free quotes and advice so it's worth a go and you have nothing to lose! Best of luck! Dave - DrainMedic