He told me that I need my pump, immersion heater and possibly either Timer or thermostat replacing. He came and look at it for 5 minutes, then charged me £69 for coming out to my house. He will charge me again for the labour and materials once I agree to have it done.
I told him that both my immersion heater and pump are working. He can even hear it himself. He said because I have an old boiler, they need to be changed at the same time and hopefully sort my CH. I disagreed to his diagnosis so that is the reason I came to this forum.