HELP ! ! ~ air in system ~ bleed weekly ~ rads now cold

[worried pete]

PLEASE HELP ........ Complete novice

Having a major headache with the central heating !
Condensing boiler ~ Fine ~ warms water no problem
Rads ..... hot when they feel like it ! .....Grunfos pump hot surrounding pipes cool ! ( suspect overheating )
Have checked its turning by removing the center steel screw.... and everything is OK
When i bleed the rads ( @ 3 times a week ) on the worst rad the air hisses out for @ 10 secs ..... then dies off ( i guess at this point air may be getting sucked in ? )
so i suspect water not getting to the pump ..... now this is where i get lost / stuck !

Do i need check the tank / ballcock / pipes ?

Any help in this direction would be most welcome !
Thanks in adavance
Worried Pete!

 

[manortim]

when you bleed the system next time, hold a naked flame to the point where the air escapes, if it ignites, it is hydrogen I.E corrision in system. power flush would be best, but compete drain down and double does of inhibitor may cure.

could be the pump/pump valves causing air to be sucked in.
could be system setup allows air to be sucked in by the pump due to blockage in system.

try connecting mains cold water feed directly into the vent pipe on the header tank using a flewi hose, open the mains water supply and BLAST mains pressrue into the system to clear any blockage/air lock.

if in any doubt as to your capabilities, DON'T BOTHER!

 

[JohnD]

.....Grunfos pump hot surrounding pipes cool ! ...

then it is not circulating water

when you bleed the rads air might come out first, them water should squirt out. Does it? What colour is the water?

what pressure is the boiler? does it vary?

you say a condensing boiler, so I don't suppose you have a feed and expansion tank - right? If you do, have you looked to see how full it is, and how muddy?

 

[worried pete]

Thanks for the help guys ...... solved at last !

It was a blocked outlet from the expansion & feed tank !

Would not of found it without your help

System running sweet ! !