How to Fix a Shower Not Getting Hot
Last updated: 30 September 2026
Check the boiler temperature, check the thermostatic cartridge, check the hot water supply, and check for mixer valve issues.
Overview
A shower that will not get hot is a common problem. This guide covers diagnosing and fixing low temperature or fluctuating shower temperature.
Step-by-Step Fix
Before beginning any repair, ensure you have isolated power or water supplies. Clear your workspace, gather standard hand tools, and wear appropriate personal protective equipment (PPE).
- First check whether other hot taps in the house are working correctly. Run the hot tap in the bathroom sink and the kitchen. If the sink tap is hot but the shower is not the problem is with the shower itself. If no hot water is reaching any tap the issue is with the boiler or hot water system.
- Check the boiler temperature setting. The boiler should be set to at least sixty degrees Celsius for hot water. If the boiler setting has been reduced the shower will not get hot enough. Increase the temperature on the boiler control panel.
- If you have a combi boiler check that it is firing when the shower is turned on. Combi boilers heat water on demand so the boiler should fire up as soon as the hot tap is opened. If the boiler does not fire the issue may be with the boiler flow sensor or diverter valve.
- Check the thermostatic cartridge in the shower valve. The cartridge mixes hot and cold water to maintain a stable temperature. If the cartridge is scaled or damaged the shower may run cold. Remove the cartridge and soak it in white vinegar for several hours to dissolve limescale.
- Inspect the cartridge seals for damage. Worn seals can allow cold water to mix with hot water reducing the temperature. Replace any worn seals with new ones and apply silicone grease before reassembling.
- If the shower has a manual mixer valve rather than a thermostatic valve the problem is usually with the internal cartridge or the non return valves. Check that the non return valves are working. They prevent hot and cold water from crossing over in the valve.
- Check the isolation valves on the hot and cold supplies to the shower. Ensure both are fully open. A partially closed hot isolation valve will reduce the flow of hot water and the shower will not get hot enough.
- Check for any recent plumbing work or changes in water pressure. If the cold water pressure has increased the shower may struggle to balance the temperature. A pressure reducing valve on the cold supply can help.
- If you have checked all of the above and the shower is still not getting hot there may be a problem with the boiler or the hot water cylinder. Call a Gas Safe registered engineer to investigate the hot water system. Do not attempt to work on the boiler yourself.
Common Symptoms & Diagnostic Resolutions
Review the common error codes and operating symptoms below to quickly identify the root cause of the fault before ordering replacement parts.
| Symptom / Code | Likely Root Cause | Recommended Resolution |
|---|---|---|
| Shower runs cold | Thermostatic cartridge failed or scaled up | Remove the cartridge and clean with vinegar. If the shower still runs cold replace the cartridge. |
| Shower fluctuates hot and cold | Cartridge failing to regulate temperature or pressure imbalance | Clean or replace the cartridge. Check for pressure imbalance between hot and cold supplies. |
| No hot water anywhere | Boiler fault or hot water cylinder issue | Check the boiler is firing and set to the correct temperature. If the boiler is not firing call a Gas Safe engineer. |
| Hot water at sink but not shower | Shower valve or cartridge problem | Clean or replace the thermostatic cartridge. Check the isolation valves are fully open. |
Frequently Asked Questions
Why is my shower not getting hot?
A failed thermostatic cartridge a boiler that is not firing correctly a partially closed hot isolation valve or a pressure imbalance between hot and cold supplies are the most common causes. Check the sink tap first to narrow down the issue.
Can I fix a shower that is not hot myself?
You can clean or replace the thermostatic cartridge and check the isolation valves. If the problem is with the boiler or hot water system you should call a Gas Safe registered engineer.
Why does my shower go hot and cold?
Fluctuating shower temperature is usually caused by a faulty thermostatic cartridge or pressure imbalance between hot and cold supplies. Cleaning or replacing the cartridge often resolves the issue.
How often should a thermostatic cartridge be replaced?
A thermostatic cartridge typically lasts five to ten years depending on water hardness. In hard water areas cartridges may need cleaning more frequently with vinegar to remove limescale.