Central heating dilemma

Keep_pedalling

Albermarle said:

I hope your house is very heavily insulated or you won't see much higher temps than 19 degrees on your heat pump instal

The current problems the OP has with their CH system struggling to keep the house above 19 degrees, could be a good way to get used to what it will be like with a heat pump !

True, my wife already suffers with Raynaud's which affects her hands, however does not mean the whole house needs to be kept at 24 degrees. An electric throw keeps her more than toasty on in the evenings.

Veteransaver

I'd try setting the pump speed to its maximum setting and then either try and drain down the system and refill, or remove radiators one at a time and flush outside with a hose, though that is very time consuming and heavy work (watch out for getting sludge over your carpets though!)
Is your system a mains fill , or gravity fill (ie with a header tank in the loft?)
If you have a header tank, check that that isn't empty (often the ball valve can stick shut), or that the breather pipe isn't in contact with the water in there.
Header tanks often get sludged up too, so worth cleaning that out if it is. Check it before draining down or reconnecting any rads as you could just end up sending more sludge down into the system.
If you are running the pump at full speed also check the system isn't overpumping (where you get frequent spurts of hot water coming out the breather pipe for the header tank)