New boiler installed but radiators cold downstairs

If you only have 3 radiators upstairs and two downstairs I’ll be suprised if balancing is the issue. Make sure the pump valves are fully open and if any isolation valves on the boiler which if it’s a system boiler there will be and if it’s a combination boiler there will be make sure they are fully open . Otherwise probably stick trvs on the radiators but if all the radiators worked before the new boiler was fitted then it’s unlikely they have suddenly stuck . Also check the new filter as if they havnt cleaned it properly that could be restricting the flow

The filter should be where it is for best protection of the boiler . I know they are unsightly but that is the best place for it

All sorted and I got a smart thermostat for free.
Boilerplan have turned this around

Thank you again to those that posted helpful comments