First of all, the Ideal E-Type looks as if it will go on forever! There are lots about, plenty of spares and many in their late twenties early thirties are still going strong.
Your problem. The Grundfos 15-60 is designed for a maximum hight of 5 meters (16 foot 3 ish) You say its only two years old, I suggest fitting a similar pump at about 4 meters to help carry the load to the top radiators.
You didn't mention the distance between the Grundfos and the top of the highest radiator but I imagine it is around 7 meters?
After seven years of miserable winters I imagine you have tried everything.But!
Try turning off all the radiators except the very nearest to the boiler and the highest, turn the boiler stat and room stats up to maximum and starting at the back of the boiler check the temperature of the pipe it should become too hot to touch very quickly keep the other hand on the return pipe and see it it too becomes too hot to touch.
If there is a clear run to the first radiator and back to the boiler the radiator will quickly become too hot to touch.
If there is an open by pass valve that is short circuiting the pipework you will soon be able to track it down.
If the water can't circulate because the pump can't cope or the pipes/rads need cleaning -then add pump, clean/flush.
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