Rayburn Driven Central Heating Problem - Upstairs Cold?

I have a Rayburn Gas CH system with a seperate pump.
The cooker / boiler is in the basement kitchen with 3 rads.
The ground floor has 4 rads.
Upstairs we have 4 rads.
All rads have TRVs fully working. System about 10yrs old in good condition.
All rads are clear of air / sludge etc.
We also have a loop in the loft tank to heat the domestic water.
The problem is that the 4 upstairs(bedroom) rads only work when the downstairs 7 rads are turned off at the TRVs either manually or when the temperature switches the TRVs off.
Could it be that the pump is not strong enough to lift the water up to the upstairs?
Last 2 winters the pump sounded awful frequently. Also when we turned the boiler temp up above 70deg it sounded like a poltergeist was thrashing all over the pipework with a hammer. It was pretty loud the higher the temp.
This autumn it's all been quiet but only partially working.
Any ideas please greatly appreciated.
PS I'm not sure how effective the system is on the domestic hot water as we do use an immersion heater also.