There are several reasons why your boiler is not working or heating the radiators when the hot water is on, such as a faulty motorised valve, diverter valve, airlocks, low pressure, faulty thermostat, electrodes, gas valve or a faulty pump
If your boiler pressure is too low, it won’t be able to heat the water properly. Check the pressure gauge – it should read between 1.0 and 2.0 bar.
A broken or mis calibrated thermostat might not be correctly communicating with the boiler. This results in the water not reaching the desired temperature.
Trapped air in your heating system can block water flow, leading to a lack of hot water. Bleeding your radiators can resolve this.
The diverter valve is responsible for directing hot water to your taps or radiators. If it’s faulty, your boiler may prioritise heating over hot water, or vice versa.
In colder months, the condensate pipe might freeze, blocking the system and causing the boiler to lock out. Sometimes the condensate pipe can be blocked even in the summer due to debris being trapped in it. Blockages in the condensate trap or pipe will cause the boiler to shut down.
If your central heating pump has failed and seized up, it will not be able to circulate hot water around the system which will cause your boiler to overheat and lockout. This can happen if you have left your boiler and pump off for long periods, causing the pump to dry out and seize up.
Electrodes are crucial for igniting the flame in a gas boiler. If they are dirty or faulty, they may not generate a strong enough spark to ignite the gas, leading to:
No ignition: The boiler will not start.
Intermittent ignition: The boiler may start but then shut down repeatedly.
Weak flame: The flame may be flickering or unstable.
What happens: The gas valve controls the flow of gas to the boiler. If it is faulty or if there is no gas supply to the property, the boiler will not be able to ignite or maintain a flame. Symptoms include:
No ignition,
Intermittent ignition whereby The boiler may start but then shut down repeatedly.
Weak flame: The flame may be flickering or unstable.
Gas smell: If there is a gas leak, you may smell gas.
If there is no gas supply or the gas has been cut off to the property, you will need to contact your gas provider
If the pressure is low, you can adjust it by using the filling loop, following the manufacturer’s instructions. If you’re unsure, contact a professional.
If airlocks are the issue, bleeding your radiators can help release the trapped air, allowing hot water to flow smoothly again.
Ensure the thermostat is set to the right temperature and replace batteries if it not a mains wired thermostat. Replacing an old or faulty one may be necessary and a relatively inexpensive fix. You may consider upgrading to a smart thermostat such as a Hive or Nest, at this stage.
A faulty motorised valve or diverter valve in Combi boilers, requires an engineer to diagnose and replace it, particular in Combi boilers as the divertor motor is contained within the boiler.
Gently thaw a frozen condensate pipe by pouring warm water over it. Be careful not to use boiling water as it may damage the pipe.
Check that your central heating pump motor is turning and not corroded and seized up. An external pump for example a GRUNDFOS UPS3 universal pump can be checked by you. In a system boiler the pump is internal to the boiler and will have to be diagnosed by a boiler engineer.
An engineer can remove the electrodes, clean it to remove dirt and debris that may be preventing a proper spark, but if the electrodes are damaged they will need to be replaced. Electrodes are not an expensive part and costs approximately £45
Gas valve: If the gas valve is faulty, it may need to be replaced by a gas engineer.
If there is no gas supply or the gas has been cut off to the property, you will need to contact your gas energy provider
Low pressure can be due to a leak in the system or the need to repressurise your boiler.
It’s recommended to service your boiler annually to keep it running efficiently.
If your boiler keeps turning off unexpectedly start by checking the pressure gauge and top it up to 1.5 bar.
If the issues persist, it’s best to call a professional gas engineer to inspect the system and resolve the problem.
If you’re dealing with boiler troubles, don’t wait for it to get worse! Our experienced engineers are ready to diagnose and repair your boiler issues. Contact us today for a reliable and affordable solution – because when it comes to keeping your boiler running smoothly, we’ve got you covered!
20th August, 2026
18th March, 2026
