Worcester 35Cdi Air Pressure Faults

Hi,  My Worcester Bosch 35CDi is showing an air pressure fault (light flashing).  Can you help?



Hi Stephen,

This could be a new problem or a problem from install.  Check that your flue is greater than 1m and ensure the restrictor has been removed.  Check that your air pressure switch is not faulty and is functioning correctly.  Check your fan to ensure it is working correctly.  Check the air pressure tubes as they may be blocked, bent and damaged causing a restriction in air flow.


My Worcester Bosch Boiler is Overpressurising

Hi,  My Worcester Bosch Boiler is overpressurising causing a trip.  We set the pressure at 1.5Bar, but then it increases to as much as 3-4 bar.  What is causing this?



Hi Brett,

You are getting mains water pressure into your boiler system.  This is caused by a number of components.  You may have corrosion/erosion in your heat exchanges causing the high pressure to enter the low pressure pipework.  You may also have a failed expansion vessel diaphragm.  Check these items with a service engineer.


CDi Boiler Not heating Water

Hello,  My Worcester Cdi boiler is not providing any heating at all.  Can you help.



Hi John,

The most common problem with the Worcester Bosch CDi series boilers not heating water is that the Central heating control knob can break as it sometimes interferes with the PCB.

Check that and let me know how you get on.


Poor Hot Water from Worcester Bosch 24CDi



I own a Worcester Bosch 24Cdi and we are getting luke warm water in our shower.  I have ran the kitchen taps for 5-10 minutes and we get no more temperature.  Do you know what is causing this and how we can fix it? Regards Jenny


Hi Jenny,

Low temperature water can be caused by many things.  The most common for your boiler is the diverter valve is passing.  This can be fixed by either replacing the diverter valve or servicing the existing.

Another issue could be a faulty hot water sensor.  You can check the sensor and if required replace.

The final check is that your heat exchanges are not blocked, as this will reduce the efficiency of the system and provide you with low temperature hot water.




WB CDi Lockout


I have a Worcester Bosch 28CDi and the boiler keeps starting then enters lockout.  The boiler light is flashing also.  Can you help me solve this problem?




Hi Doug,  These types of boilers will lockout if your gas valves is sticking or is set too low starving your boiler of gas.  Also you may have a problem with your sensing leads.  Another issue could be that you are getting moisture in your PCB causing the low voltage connection to action the lockout.

Hope this helps.