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. ⌄
- Pipe drips continuously outside
- Drip occurs only while heating
- Water tank level is too high
- Discharge is hot
- Dripping began after pressure work
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 — Identify which system the pipe serves Use visible controls only and stop if pressure or temperature is unsafe. ⌄
Process
Trace whether it comes from a cistern, boiler or hot-water system.
Step 2 — Check timing and temperature Use visible controls only and stop if pressure or temperature is unsafe. ⌄
Process
Note whether discharge occurs during heating and whether the water is hot.
Step 3 — Check accessible cistern level Use visible controls only and stop if pressure or temperature is unsafe. ⌄
Process
For open tanks, observe whether the float valve closes normally.
Common causes explained Why hot-water systems lose heat, overheat or discharge. ⌄
A dripping overflow or warning pipe may indicate an overfilling cistern, failed float valve, expansion problem, relief-valve discharge or overheating.
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. ⌄
- Test float valves and water levels.
- Check expansion vessel charge.
- Test pressure and temperature relief valves.
- Inspect thermostats and controls.
- Verify discharge pipe arrangement.
Parts that may need replacing Common components linked to this fault. ⌄
- Float valve
- Expansion vessel
- Pressure-relief valve
- Thermostat
- Discharge component
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.