🔍 No Hot Water — Common Causes
| Scenario | Likely Cause | Fix |
|---|---|---|
| No hot water, heating works | Faulty diverter valve (combi boiler) | Engineer required |
| No hot water or heating | Boiler fault, pressure loss, thermostat | Check pressure, call engineer |
| Hot water lukewarm | Faulty thermostat, part-failed diverter | Engineer required |
| Hot water runs cold | Diverter valve, heat exchanger scaling | Engineer required |
| No hot water (system boiler) | Immersion heater, zone valve, cylinder stat | Check immersion, call engineer |
🔧 Heating Works But No Hot Water — Diverter Valve Fault
If your heating works fine but you have no hot water from the taps, on a combi boiler the most likely cause is a faulty diverter valve.
The diverter valve directs hot water either to the radiators or to the taps. When it fails, it gets stuck in one position — usually sending all the hot water to the radiators.
Signs of a faulty diverter valve:
• Heating works fine but no hot water from taps
• Hot water works but heating doesn't (stuck the other way)
• Water lukewarm even when boiler is running
• Boiler making a humming noise when hot water is demanded
• Heating works fine but no hot water from taps
• Hot water works but heating doesn't (stuck the other way)
• Water lukewarm even when boiler is running
• Boiler making a humming noise when hot water is demanded
Diverter valve replacement typically costs £150-300 and can usually be done same day by FE Maintenance.
🏠 No Hot Water with a System Boiler & Cylinder
If you have a system boiler with a hot water cylinder (not a combi boiler), the cause of no hot water is different:
- Immersion heater fault — the backup electric element in the cylinder has failed
- Cylinder thermostat fault — cylinder not heating to the correct temperature
- Zone valve fault — the valve controlling hot water flow to the cylinder is stuck
- Motorised valve failure — common fault, relatively inexpensive to fix
Quick check: Press the boost button on your hot water cylinder. If you get hot water after 30-45 minutes, the immersion heater is working but your boiler isn't heating the cylinder — likely a zone valve or programmer fault.
Frequently Asked Questions
On a combi boiler, having heating but no hot water usually means the diverter valve is stuck in heating mode. This is a common fault that FE Maintenance can fix same day. On a system boiler with a cylinder, the issue is likely a zone valve, cylinder thermostat, or motorised valve. Call 020 8445 1303.
Most no hot water faults can be diagnosed and fixed in a single visit of 1-3 hours. Diverter valve replacement takes about 1-2 hours. Zone valve replacement takes about 1 hour. FE Maintenance offers same-day appointments — call 020 8445 1303.
If you have an electric shower, it works independently of the boiler and should still work. If you have a mixer shower or power shower, you'll need the boiler working. You can also boil water and use a bowl wash until the boiler is repaired.
Sudden loss of hot water is usually caused by a component failure — diverter valve, zone valve, or the boiler itself locking out due to a fault. Check the boiler display for error codes and the pressure gauge. Then call FE Maintenance on 020 8445 1303 for a same-day fix.
Cost depends on the cause. Diverter valve: £150-300. Zone valve: £100-200. Motorised valve: £80-150. Immersion heater: £100-180. FE Maintenance provides a fixed quote before starting work. Call 020 8445 1303.
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