Hot-water systems can involve scalding water, mains electricity and pressurised cylinders
Do not remove boiler covers, immersion-heater covers or adjust unvented-cylinder safety devices unless qualified. Hot discharge, overheating, heavy tundish flow or cylinder leaks need urgent attention.
MOST LIKELY CAUSES
Start with these
Symptom variations Match the temperature, timing and system behaviour. ⌄
- Water around cylinder base
- Drip from immersion heater
- Leak worsens while heating
- Green or rusty staining
- Water appears from cylinder casing
Quick checks Use user controls and visible observations only. ⌄
- Check whether all hot outlets are affected.
- Identify whether the system uses a boiler, cylinder, immersion heater or a combination.
- Review visible timer, thermostat and boiler status indications.
- Note whether the problem occurs during heating, after heavy use or continuously.
- Stop if water is dangerously hot, leaking or discharging through a safety pipe.
Step 1 — Turn off the heat source Use visible controls only and stop if pressure or temperature is unsafe. ⌄
Process
Switch off boiler hot-water demand and immersion heaters.
Step 2 — Identify whether the leak is a joint or cylinder body Use visible controls only and stop if pressure or temperature is unsafe. ⌄
Process
Dry the area and trace the first wet point.
Step 3 — Isolate water if the leak is worsening Use visible controls only and stop if pressure or temperature is unsafe. ⌄
Process
Use the appropriate safe supply isolation.
Common causes explained Why hot-water systems lose heat, overheat or discharge. ⌄
Cylinder leaks may come from pipe connections, immersion heaters, thermostatic valves, drain cocks, relief components or corrosion through the cylinder body.
Hot-water faults can involve the heat source, storage cylinder, controls, mixing valves, circulation pipework or safety devices. The exact system type determines the safe repair path.
Advanced diagnostics Plumber or heating-engineer checks. ⌄
- Inspect and remake pipe connections.
- Replace immersion gasket or heater.
- Test expansion vessel and relief valves.
- Assess cylinder corrosion.
- Drain and replace failed cylinder safely.
Parts that may need replacing Common components linked to this fault. ⌄
- Immersion gasket
- Immersion heater
- Valve or joint
- Expansion vessel
- Hot-water cylinder
When to call a plumber or heating engineer Conditions that should end basic troubleshooting. ⌄
- Water is dangerously hot or the system appears to be overheating.
- A tundish or warning pipe is discharging hot water.
- An unvented cylinder or safety valve is involved.
- The cylinder body, immersion heater or boiler is leaking.
- Electrical testing of immersion or boiler controls is required.
- The fault persists after checking normal user controls.
Frequently asked questions Common questions about hot-water faults. ⌄
Why does hot water run out faster than before?
The cylinder may not be heating fully, an immersion element may have failed, or demand may exceed the stored volume.
Why is a tundish dripping?
It shows that a safety valve is discharging, often because of expansion, pressure or overheating faults.
Can I turn up the thermostat to fix lukewarm water?
Only normal user settings should be adjusted, and never beyond safe manufacturer guidance. Persistent faults need testing.