Boilermate2000 No Hot Water

Been reading through the topics for something similar to my issue, there's a few but I'm hoping for something a bit more categoric.

I have just replaced the ACB on my Boilermate, the CH wasn't switching off, but that now seems sorted, however, the initial issue, (which seemed to kick it all) a lack of hot water without switching to 'emergency' still exists.

The header tank doesn't seem to be filling as I feel it should, and even if I do it manually, the water is still stone cold.

Question: If I fill the header tank manually, by pushing the arm down, how long should I be waiting before trying the hot water again.

Is there anything else I can try to diagnose the problem?

I will call a plumber out, but hoping, after a £250 outlay for an ACB, I can save some money.

All suggestions welcome, thank you

Why do you feel that header tank is not filled as should be? If you want to check if your main tank filled then you will need to get some water out from the system and see that header tank lost same amount of water(block the arm not to fill it automatically). If not then most likely that pipe between header tank and main tank is blocked. By the way, the water in my header tank is warm, so either your header tank not "connected" with main tank and not enough water in system or your boiler doesn't work. So anyway, best to check first if system is full.
If full then search for similar problem on the forum regarding sensors, scaled PHE...can't remember other reasons apart from PCB you changed.
And check temperatures on display before hot tap open and during