LE can also be a faulty overheat stat,on the Icos the oh stat is up near the top of the boiler,and if the connectors above leak water/crud can run down to the stat.
LF is flame detection,as already mentioned.
i would be happy to try new ways,the crimping method appears to be a good way,particularly as many buildings now will not allow the use of naked flames,for soldering.
Like many ive been a bit of a stick in the mud,preferring to use e/feed soldered,although i have used plastic and push fit...
You have to remove the fan and burner,even then its not easy,use a pair of grips to remove it,and refit the new one,i made a special tool,cos i was changing them all the time, a sort of socket that fitted on the AAV perfectly,that made it easy.
If you think OPs post was good,which it was by the way,i worked a fair few years ago for the water company,there was a sorry saga invloving a shared supply which was turned off leaving a certain woman without water,it carried on over the course of a weekend with road gangs out trying to run temp...
Last year i changed about 6 Honeywell 3 port valves that were "clonking"
there was a faulty batch apparently,which move too quickly causing a clonk which vibrates through the coil in the cylinder,and other pipework.
In all cases,swapping the valve for a new one was a complete cure.
Get them back.
THE PROBLEM IS NOT "NORMAL" It is your landlords problem to sort out,you have rights as a tenant,so dont be fobbed off.Withdraw payment of part of your rent until its sorted to your satisfaction,if its costing you a mint bacause of using additional heating,keep a detailed record of how much,then...
Yes it looks like its leaking from the sump joint,this is non repairable,and will need replacing.
Ive started to lose track here, i thought you had a problem with the boiler making a noise to start with,and were calling Ideal out on a fixed price repair?
Well if you rang up for a fixed price repair he should have booked it in to have the heat exchanger replaced,they should let you know in due course when they are coming to do it.