Ideal Icos Not Lighting Flashing LF

I received a call from a gentleman because his boiler was not lighting at all and was flashing the letters L and F on the display. From this information I knew he had an Ideal Icos as it is a common fault on these boilers. The fault is due to flame failure either at the ignition stage or rarely whilst the boiler is running.

I fired up the boiler and it went through the lighting process but did not light, the fan ran for a while before attempting to light again. It attempted to light three ties before going back to alternating 'L' 'F' on the display.
Each time it attempted to ignite I could hear it sparking.

I took the case off the boiler and removed the fan and burner so I could look at the electrodes as it common for them to become dirty or distorted. They looked ok, but I removed them for a closer look and a quick rub down with some abrasive. I re-assembled the boiler before trying to light it again but it was still the same.

I checked the gas pressure which was fine and the pressure was dropping as the gas valve opened and so I knew that the gas valve was working ok. I switched off the gas at the isolation valve and removed the spark electrode from the combustion chamber. I then lit the boiler with the spark electrode in a position where I would be able to see the strength of the spark. When the boiler went to the ignition stage I could hear the spark being generated but there was no spark at the electrode. Either the ignition lead was faulty or there was a problem with the spark generator. There did not look to be any issues with the ignition lead and so I replaced the spark generator.

Both of my local Parts Centers had more than one in stock which makes me think that it is not uncommon for the spark generator to fail. Their part number is 498866 or the Ideal part number of 173538. The boiler was working well again after I remembered to turn the gas back on to the appliance :-).

Disclaimer: The works described in this blog are a record of work undertaken and should not be taken as guaranteed to solve your problem. Work should only be carried out by persons qualified and competent to do so.