If your property has two or more showers, it might be irritating if one is cold while the other works as it should, or if temperatures fluctuate.
Fluctuating shower temperature is a common issue, even when a property has just one shower.
Here’s how to diagnose and fix inconsistencies in shower temperature.
First, check your taps
Before trying anything else, it’s vital to identify whether the issue is associated with the showers or the shower and taps. If taps are also affected, that signals a wider systemic issue with the heating system and/or boiler.
To diagnose the issue with your hot water, it's important to first test your taps to determine if the problem is isolated to just the shower or if it affects the entire house.
Start by turning on your hot water taps one at a time and observing if they heat up as you’d expect. If your taps become warm as they should, the problem is likely isolated to the shower system.
However, if your taps also remain cold or the temperature fluctuates beyond reasonable limits, there could be a variety of possible causes. It’s worth noting that the temperature may fluctuate a bit before it stabilises.
First, try shutting off the boiler and resetting it. If the problem persists, the issue may be caused by a range of other factors, including the thermostat, the clock, the boiler timer, leaks or airlocks in the pipes, frozen pipes or boiler pressure issues.
In these cases, it’s probably necessary to call a plumber to diagnose and repair the issue.
Reasons one shower is colder than the other
1: You’ve used up all the hot water
If you have a heating system with a hot water tank (typically installed in an airing cupboard), then you only have a finite hot water supply for showers.
Once the hot water is used up, you’ll need to wait until it’s replenished. If multiple people take showers in sequence, and there are two or more showers, or a shower and a bath, etc, then hot water will drop to one before the other. This is because the shower closest to the hot water tank will likely drain the hot water first, leaving less for the second shower.
A typical hot water tank should be fine for two to three standard-length showers, but if someone is hogging the shower for a long period, there simply won’t be enough hot water left over. You can also check out our article on common hot water cylinder problems.
You might need to schedule or plan your showers (e.g. if there are three or more people in the house).
However, if this is a chronic issue that can’t be sorted by planning showers, then it’s possible to fit a larger hot water tank, though this is an expensive solution.
2: Individual faults for each shower
If one shower seems to be not working properly while another is fine, there may be an issue with that particular shower. Here are some common issues that apply to all showers:
- Mixing valve problems: The mixing valve controls the ratio of hot and cold water that enters the shower. If it's not functioning properly, the shower temperature may fluctuate. The valve might be set up incorrectly, damaged or blocked.
- Low water pressure: If the boiler pressure is low, it can cause the shower temperature to fluctuate. This can be caused by leaks or issues with the pressure release valve. See our article on fixing low pressure showers.
- Air in the system: A build-up of air in the system can cause the shower temperature to fluctuate, though it’s more likely to cause the water to spit or flow unevenly. Bleed the radiators and see if that helps.
- Shower head: If the shower head is clogged or has a build-up of mineral deposits, it can cause a restriction in the flow of water and can also affect the temperature. Shower heads can also suffer from a buildup of air. Further, very large shower heads can place additional demand on the heating system, which is especially problematic with combi boilers. See if the issue persists with a smaller shower head.
- Diverter valve issues: If you have a multiple shower head or a shower/tub combination, a diverter valve is used to redirect water flow from one outlet to another. If the diverter valve is not functioning properly, it can cause temperature issues and fluctuation. To fix, the diverter valve may need to be adjusted or replaced.
3: Mixing valve broken
Faulty shower mixing valves are a leading cause of shower malfunction. Mixing valves mix hot and cold water to output the desired temperature.
Newer mixing valves are thermostatically controlled, which sets the water temperature at the desired level before it reaches the shower head. So, if you’ve recently installed a new shower with a thermostatic valve, the valve may have been set up improperly.
If you have a standard mixing valve, there could be a blockage, or internal parts might wear down. You can try to repair the mixing valve, e.g. by replacing any worn or broken o-rings.
Otherwise, you might need to replace it.
3: Check the boiler
The fault may lie in the boiler and not the showers. Fluctuations in water demands can cause combi boilers to produce erratically heated water, especially when their output is marginal for the pressure demand.
In other words, if you’re running two showers on a combi boiler that is barely cut out for that demand, it will likely struggle to heat the water steadily. This can result in wild temperature and flow fluctuations. This is especially common when one shower has a high-pressure demand, e.g., a large shower head.
This is also called boiler cycling. When the boiler cycles, it constantly fires on and off, resulting in fluctuating water heat. If you’ve purchased a larger shower head, that may be the issue.
Otherwise, you might be expecting too much of your combi boiler. Get in touch for more help.
