condensing pipe was frozen I defrosted it now the boiler want fire up not sure what to try next cant get engineer for two days any suggestions

stuart scobie, December 2010

Had the the same fault after draining. Rectified by lightly sandpapering the condensate sensor and a wipe with a rag wetted with DW40, fired up great after the clean as the sensor was coated with a very fine dusty looking coating due to the corrosive condensate backup.

Wudz, January 2012

I have been having this problem intermittently for the last month. My engineer tells me that, apart from the condensate outlet being blocked or frozen, some other causes of AL10 can be the ignition sensor (gap too big), a faulty gas valve, moisture in the plastic pipe from the gas valve to the boiler compartment (pull it off and blow through it), or water or dirt in the gas supply (possibly caused by corrosion inside old iron "gas barrel" pipework). It's also possible that there is a fault in the electronic control board but my engineer disagrees and says that PCB faults always come up as AL55

Nick Waller, December 2011

I've got the same problem - its probably your condesate sensor. It will have been submerged in water due to the condensation backing up (couldn't escape due to the frozen pipe)
and filling the tank over the required level. Only solution I've found is to get a new condensate sensor - still waiting for one to be sourced.

Paula, December 2010