If your boiler is running but not producing hot water, the cause is often pressure imbalance, thermostat settings, or internal component issues rather than total boiler failure.
Before assuming a major fault, it helps to check a few common causes.
The Most Common Reasons This Happens
1. Low Boiler Pressure
Most boilers require adequate system pressure to circulate hot water. If pressure is too low, the boiler may run but fail to heat water properly.
If pressure appears low, see:
→ Why Is My Boiler Pressure Low?
2. Thermostat or Programmer Settings
Incorrect settings on the thermostat or timer can prevent hot water from being activated.
Check whether hot water is scheduled or manually switched on.
3. Diverter Valve Fault (Combi Boilers)
In combination boilers, the diverter valve directs heat either to radiators or hot water taps. If it becomes stuck, you may get heating but no hot water.
4. Air in the System
Trapped air can reduce circulation and affect heating efficiency.
If radiators are also not heating evenly, see:
→ Why Is My Radiator Not Getting Hot?
5. Faulty Heating Element or Sensor
Internal components such as temperature sensors or heat exchangers can fail over time, preventing proper heating.
If the boiler is also making unusual sounds, see:
→ Why Is My Boiler Making a Noise?
Is This Normal?
It may be minor if:
- Pressure is slightly low
- Settings were recently adjusted
- Only hot water is affected
It may require attention if:
- The boiler shuts off repeatedly
- Pressure keeps dropping
- There is no hot water at all
What You Can Do
If your boiler is not heating water, you can:
- Check the pressure gauge
- Review thermostat and timer settings
- Reset the boiler safely
- Observe whether radiators are heating normally
If hot water does not return after these checks, professional inspection may be required.
For more related issues, see: