Match what you notice
- It changes temperature with no other taps running
- On an older thermostatic mixer, we start by checking the thermostatic cartridge. It adjusts the mix as the incoming conditions change. If it sticks or stops responding properly, the temperature can wander even when you leave the control alone.
- It changes when another tap runs or a toilet refills
- Using another outlet can change the pressure or flow available to the shower. We check the hot and cold supplies under use. Some mixer models have inlet check valves that prevent water flowing backwards. Where fitted, we check these if the symptoms point to a supply imbalance.
- The temperature changes and the spray has become weak
- Tell us if the two changes started together. Scale at the shower head or a restricted hose can cut the flow. We can check the flow at the mixer and compare it with the flow through the hose and head.
- Hot water also varies at other taps
- Mention which outlets are affected and whether the issue started after work on the water supply. This helps us decide whether to focus on the shower or investigate a wider supply issue.
What to tell us before a visit
Stop using the shower if the temperature jumps unexpectedly, especially if the water becomes very hot. Tell us whether it happens from the start, after a few minutes or when another outlet runs. A photo of the controls and any visible brand or model helps us identify the mixer.
What AquaFix can check
We assess the cartridge, the flow at the shower and the hot and cold supplies. Where a fault is confirmed, the make and model help us identify a compatible part. For a concealed mixer, we check whether it can be serviced through the trim opening. If the valve body needs replacing, we discuss access and making good before opening the wall.
Read about shower pump problems
Further reading
- Mira guidance on mixer showers that fluctuate between hot and cold
- Bristan guidance on thermostatic valves and replacement cartridges