heating problem boiler/water pump?

[DazF1]

drained system to repair valve filled system (open system)
boiler fires up but only stays on 1 0r 2 mins then knocks off
bled system loads still happens put hose pipe to drain valve on rad open valve whilst like this boiler lights and stays on any suggestions
gloworm space saver 50 mk2 wall mounted smc comet 2-130 pump
pump gets very hot

 

[seco services]

airlocked pump

 

[spacethegas]

when you bled system does water come out eventually from all vents ?
if so airlocked.
if not, blocked cold feed.
either one it would be best to get someone in.
i know how i would tackle both problems but i couldn't advise you how to do so as there are potential problems that may arise.

 

[liverpoolboy]

surely if when bleeding all air vents (rads/pump/man air vent) if water comes out then there will be no air lock!!!

 

[spacethegas]

liverpoolboy
there may be high points within the system that do not get vented.

DazF1
on reflection. your pump is very old & it sounds like that is the area to investigate.

 

[liverpoolboy]

usually the manual air vent is at the highest point, just tee'd off above the primary flow to the hws cylinder.

bleed the pump and maybe even disconnect and replace/clean out.