The man from Gledhill - who make the Boilermates - came out on Friday and virtually replaced everything in the Boilermate - which now works both normally and on emergency heating and hot water.
We did have the boiler working for a time - in spite of the absence of the installer who again failed to turn up on Friday. The boiler is now having a hissy fit again and we're back to the emergency heating. We are not letting anyone else touch the Boilermate again! Full marks to Gledhill - they've done a brilliant job and he had all the parts he needed with him - which seems to be pretty unusual these days.
Personally I suspect a fault with the only bit of the system which hasn't been replaced - the oil line under the ground from the tank to the house. This was supposed to be replaced and hasn't been. We're supposed to be having a surveyor come out to check the work has been done properly so he will have his ear severely bent when he does turn up as we have an ongoing list of what's happened and not happened.
To look on the bright side we do have heating - at a cost because it's electric - and we're not cold. We shall get it sorted in the end no doubt but when is anyone's guess.