I have an alpha he cb33 boiler which has stopped working this morning. Yesterday I removed a radiator for cleaning then put it back on and re-pressurised the system. It was working ok last night. However it is now flashing alternately between the A & B lights which indicates a pressure problem. Reading the troubleshooting bit in the servicing manual points to section K on page 41 but that doesn't mean a lot to me

So far I've tried de-pressurising and the pressurising the system again to within the green pressure zone as indicated on the face of the boiler. I've tried resetting the boiler. I've tried powering off and then on again after various lengths of time 5seconds - 30minutes. Nothing has stopped the lights flashing and boiler to reactivate.

I was wondering if anyone could recommend anything else to try before I call in a boiler engineer.

EDIT: I had an engineer around this morning and he discovered that it was the primary pressure switch, I'll update again once the repair has been made with all the required steps for testing and fixing.

  • Did you bleed the radiators? In the proper order? Sep 25, 2012 at 13:13
  • Yes, I bled all of the radiators after I put the pressure back into the system. At this stage I'm thinking that the PCB has crashed because power on/off and resetting it has no effect. When it powers back on it goes straight into the error state.
    – Neil
    Sep 25, 2012 at 13:24
  • Double check the radiators before you do that. Air may have "settled out" of the water over night. Sep 25, 2012 at 13:34

2 Answers 2


You drained and re-pressurized the system. This introduces air into the system. Section 5.1 of the manual indicates a very clear sequence of steps that should be followed to re-pressurize the system, one very important one of which is bleeding (venting) the radiators, one by one, from lowest to highest.

This is done to get air out of the system that's trapped in the radiators. Air is compressible, water is not, so having air in the lines will mess with pressure readings something nasty.

Bleed the system and check the neons again.

  • Thanks, I'll try that when I get home then update if it works.
    – Neil
    Sep 25, 2012 at 13:58

Likely that the pressure sensor is blocked from debris in the system. Removing and cleaning may well resolve your issue.

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