Boiler Shuts Down

Boiler shuts down and goes to lockout

Fault Fix
faulty pump (not at full capacity) Check the pump for signs of damage, test the electrical connections, and replace if necessary. Replace pump head
faulty fan (not at full capacity) Check / lubricate bearings
clear debris build up Replace fan assembly
blocked condensate pipe work/trap Clear blockage / ice plug or Increase pipe work fall
faulty ionisation electrode Check gap/wiring /damages
blocked heat exchanger (blocked with sludge) Replace or cleanse system
blocked primary filter on plate exchanger Clean debris from filter
faulty thermistor (losing calibration) Check / replace
faulty overheat cut out stat (losing calibration) Check / replace
faulty gas valve (faulty modureg / solenoid) Replace gas valve
blocked bypass pipe/ no bypass Adjust / install bypass
faulty air pressure switch (stuck in NO position) Replace air pressure switch

Testing the Air Pressure Switch:

  • Turn off the power to the boiler and allow it to cool down.
  • Locate the air pressure switch. It is usually located on or near the fan assembly of the boiler.
  • Remove the wiring connections from the switch.
  • Use a multimeter to check the continuity of the switch contacts. If the switch is faulty, the multimeter will not show any continuity between the contacts.
  • Check the air pressure switch tube for blockages or damage.
  • Test the vacuum created by the fan by connecting a vacuum gauge to the air pressure switch tube. The vacuum reading should be within the manufacturer’s recommended range.
  • If the air pressure switch is faulty, it needs to be replaced.

Replacing the Air Pressure Switch:

  • Turn off the power to the boiler and allow it to cool down.
  • Locate the air pressure switch and remove it from the boiler.
  • Take note of the exact make and model of the switch, as well as the pressure rating.
  • Install the new air pressure switch by connecting it to the wiring and attaching it to the boiler in the same position as the old one.
  • Make sure the air pressure switch tube is connected and free of blockages or damage.
  • Turn on the power to the boiler and test the new air pressure switch by checking the vacuum reading as described above.

It’s important to note that working on a boiler can be dangerous and should only be carried out by a qualified heating engineer.

Additionally, the specific steps for testing and replacing a faulty air pressure switch may vary depending on the make and model of the boiler, so it’s important to consult the manufacturer’s instructions for specific guidance.
faulty low water pressure switch (losing calibration) Replace / clear blockages
Low water pressure Check the pressure gauge and refill the system as necessary.
Excess air trapped within heat exchanger Check / replace air vent. Clean the heat exchanger, inspect the combustion chamber and flue.
Blocked condensate pipe Clear the blockage in the condensate pipe, check the trap and discharge point for debris.
Air in the system Bleed the radiators and boiler to remove any air pockets.
Faulty pressure relief valve Test and replace the valve if necessary.

Testing the Pressure Relief Valve:

  • Turn off the power to the boiler and allow it to cool down.
  • Locate the pressure relief valve.
  • Place a container underneath the pressure relief valve to catch any water that may be released during testing.
  • Lift the lever on the pressure relief valve to release some water. If the valve is working correctly, water will be released and then stop when the lever is released.
  • If water continues to flow after the lever is released, or the valve does not release any water at all, then the pressure relief valve is faulty and needs to be replaced.

Replacing the Pressure Relief Valve:

  • Turn off the power to the boiler and allow it to cool down.
  • Locate the pressure relief valve and remove the cap that covers it.
  • Using a wrench or pliers, unscrew the pressure relief valve from the boiler.
  • Clean the threads on the boiler where the valve was removed.
  • Apply some thread sealant to the threads of the new pressure relief valve and screw it into place on the boiler.
  • Tighten the pressure relief valve to the manufacturer’s recommended torque specification.
  • Replace the cap that covers the pressure relief valve.
  • Turn on the power to the boiler and check the new pressure relief valve for proper operation by testing it as described above.

Additionally, the specific steps for testing and replacing a pressure relief valve may vary depending on the make and model of the boiler, so it’s important to consult the manufacturer’s instructions for specific guidance.
Faulty printed circuit board (PCB) Test the PCB for faults and replace if necessary.
Faulty thermostat Test the thermostat and replace if necessary.

To test the thermostat on a combi boiler follow these steps:

  • Turn off the power to the boiler and allow it to cool down.
  • Remove the thermostat from the wall and disconnect it from the wiring.
  • Use a multimeter to test the continuity of the thermostat contacts. This will show whether the contacts are open or closed, indicating whether the thermostat is working properly or not.
  • If the thermostat is not working properly, replace it with a new one.
  • If the thermostat is working properly, reattach it to the wiring and re-install it on the wall.
  • Turn on the power to the boiler and test the thermostat by adjusting the temperature settings and checking that the boiler responds accordingly.

It’s important to note that this is not an exhaustive list of all the possible faults and solutions that could cause a combi boiler to shut down.

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