Hot Water Cylinder Problems: Find Your Symptom
Hot water cylinder problems show up as one of four symptoms: no heat, water that is not hot enough, a leak, or a valve that keeps dripping. Each points to a different part, so find your symptom below, make only the safe check, and let the fault be found before anything is replaced.
Services
Each one starts with the diagnosis, so the price is known before any work.
- Cylinder diagnosisFind the fault first£180Fixed price
- Cylinder leak repairLeaking cylinderStarts with a £180 diagnosis
- Immersion heater replacementElement and thermostatStarts with a £180 diagnosis
- Cylinder fault repairRepair by partStarts with a £180 diagnosis
No VAT is charged. There is no call-out fee.
What are you seeing?
Pick the nearest match and read the guide that answers it.
No hot water
A leaking cylinder
A dripping valve
An old cylinderNo hot water or not hot enough
This branch runs power, controls and heat source in order: supply and fuse, programmer, cylinder thermostat and cut-out, then the immersion element or the coil and its two-port valve. A timer setting or a melted fuse causes more cold cylinders than a failed part does. Start with the safe checks on hot water cylinder diagnosis, and for a failed element see immersion heater replacement.
Leaks and wet floors
Water at the base rarely starts there. It can come from a valve group joint, an immersion boss, a coil connection, a relief valve discharging, or the shell seam. All except the shell can be repaired in place. Cylinder leak repair shows how the source is traced.
Dripping valves, pressure and noise
A tundish that drips on an unvented cylinder means the temperature and pressure relief valve, the combination valve or the expansion vessel needs attention. Never block, cap or adjust any of them. Banging, rumbling or whistling can be scale on an element, a failing valve or air in the system. See TPRV and expansion vessel repair.
Symptom, likely part and first safe check
Use the list to match what you see to the first check. Only the programmer, the thermostat dial and the fuse or breaker are safe for a householder to look at. If you are unsure, the full ordered test and the worked element reading are on the same page.
- Cold taps, immersion on: fuse or spur, then thermostat, cut-out and element, which sit behind mains-voltage covers and are not householder checks.
- Cold taps, boiler on: hot water channel, zone valve, cylinder thermostat, coil.
- Water too hot: thermostat set or stuck, then the unvented safety devices.
- Wet base: valve group, boss, coil joints, then the shell.
- Dripping tundish: relief valve, combination valve, expansion vessel.
Steam or very hot water from an unvented cylinder means it is overheating: isolate the heat source and keep clear. A smell of gas means leave the property and call 0800 111 999, the National Gas Emergency Service.
Take the cylinder apart
Guides on this topic
Questions people ask
What are the most common hot water cylinder problems?
No hot water from a failed element, thermostat or zone valve, leaks at valves and joints, and a dripping relief valve on unvented cylinders. A timer or fuse fault often looks like a cylinder fault.
Do I need a new cylinder for these problems?
Rarely. Most faults are in a replaceable part. Replacement follows only when the shell is leaking or a sealed coil has failed.
Is any of this safe to try myself?
Only the programmer, the thermostat dial and the fuse or breaker. Nothing inside electrical enclosures, and nothing on relief valves or tundish pipework.