Reluctant Central Heating - Apollo Fanfare

I have a 19yr old installation based on a myson/Thorn Apollo Fanfare 30/50si. It has acquired habit of firing up and running then shutting down etc. The system has also started to produce an irritating tapping which appears to be mid-floors.
It had a new fan in April 2006 and the PCB is relatively new. I've just replaced all the 'stats [4 of them] and system it is controlled by a Dataterm EMS box of tricks, recently upgraded.
I flushed it on boxing day[yes sad git - wife's idea] and since then it has refused to give any heat upstairs, both regular and bathroom rads circuits, bar one rad in a bedroom. Downstairs seems fine.
Whilst the pump runs and I have bled and re-bled, I notice that the pump body around the the motor seem inordinately hot, far hotter than the pipework feeding it.........could this mean that whilst the pump may be spinning up to a point, that it's not actually circulating with enough welly and hence the antics of the boiler?
Thanks in advance for any useful pointers.

Pumps are cooled by the water flowing through them.

If its hot then I would expect its not pumping anything. If the impeller is still attached and its spinning then perhaps one of the pump valves is failed closed.

Tony

You say downstairs heats fine ? You could try shutting off the radiators that do heat and "forcing" the heat upstairs. Try turning the pump speed up to maximum setting till the air clears - sounds like thats all it is : airlock.

I assume your hot water works ok ? And that all was reasonably well before you flushed it ?

Or some of the gunk you dislodged by your flushing has blocked the pump.....
remove the allen screws and take the pump apart, and see if the valves are blocked...

Nice pic Was thinking that also, certainly sum kind of blockage, wether its air or sludge.

First off, thank you folks for your responses.
Having flushed the system for 45 minutes again, re-bled and re-started, it's still off/on as before, but I now have heat in all bar 1 of the normal rads upstairs. The bathroom ones on the h/w circuit are still u/s. Yes, water heats ok.
The stat and controller are all in one on the Dataterm in the hall, which won't show anything above 18 degrees.......it feels like it too.
I'll try closing down the ground floor and forcing it, then I'll probably take off the pump for a shufti.
I should of added that when I replaced the pump overrun'stat last week, the old fell apart in my hands and I know that the pump was undoubtedly running full time [never off] for goodness knows how long, so it's no wonder it may be knackered.
Thanks again.

Hi......frustrating or what. Any more advice forthcoming please. I have now replaced the pump and drained filled and bled the system. I now have heat in all the regular radiators, both up and down, which is better news. However, the 2 on the hot water circuit are still cold , despite further attempts to bleed. Their supply, which I assume is the tee-off between the pump and the y valve, starts of hot at the top, cooling as it disappear into the floor. I probably failed to mention that this boiler is located in the airing cupboard along with the tank. The digital room stat on the Dataterm controller shows that the room temp will only reach a max of 19 degrees, resisting all efforts to reach the set point, a result of it persistently starting and stopping! Other than the gas valves, I think I can safely say that everything has at some point , been replaced in the last 2 years, barring the air pressure switch, which does click when I suck/blow, though I confess that I haven't put a meter across it to check circuitry!