how can I fix my old glow worm central heating boiler model 65-80?

several months ago the ignition on my conventional flue boiler failed to stay alight and I had an idea that it was caused by a faulty thermocoupler(?). I called in an engineeer and this proved to be the case and the part was replaced and the boiler became operational again. On his departure, I thought that the heater seems to be constantly on high (listening to the flames) but took no notice.

Yesterday, I turned on the boiler and decided to have a look and was perturbed to see flames far higher than they should be, which were even coming up under the inspection plate which was completely covered with soot on the inside. The pilor light itself appears to be alright but I have not put the boiler on since as it appears to be dangerous and sounds like a roaring furnace when it's alight!

The engineer did not seem to be at all familiar with this type of floor standing conventional flue boiler. the pump is a grundfos UPS1550 130 P/N 96281426 PC 0537.

Can anyone help as I was charged £150.00 when the thermocoupler was fitted!!