problem since draining

[daza1234]

i have a glow worm space saver, since draining to replace the pump no hot water is present, it has 2 flow and 2 returns and the flow and return for the rads are hot, only cold water comes out of the hot tap.
the hot water flow from the boiler feels warm near the boiler but as you move your hand away less than a metre from the boiler the pipe gets cold.

i think there is a sludge/ air block in the boiler itsself is this possible?

is it easy to rectify?


many thanks for any replys...

 

[EliteHeat]

You have an airlock in your gravity hot water circuit. Loads on the board about it.

 

[ChrisR]

Sounds like your HW might rely on gravity circulation??

But all the rads vent water out, yes? If so, then you're fairly sure the route back to the header tank is clear - they can block.

What they used to do, but of course I can only recommend you avoid doing, because, who knows, you may be high on crack or under thirty or have teenagers, was to put the boiler on hw only and slide the thermostat phial(s) out of its(their) socket(s) in the boiler cast iron lump.
Then they watched until the boiler boiled. If the system was sound in the vent and overflow department, no problem, let it bubble for a few seconds and then turn the burner off. Put the phial(s) back in and let warm up before turning boiler back on. It would stay off for a bit.

 

[daza1234]

rads vent ok,
there is a vent above the cylender which i get cold water from - when opened.
i took the thermostat out for a short while and the pipes got very hot (boiled) upto this vent close to the indirect entry to the cylender. steam and hot water came out for a few seconds then it very quickly went cold again (as i was draining it cold water was coming down from the header tank to refill the water i had replaced)
the pipes then goes cold back to the boiler which the hot water seems to not want to leave...
is there anything else i could try...

many thanks....

 

[EliteHeat]

You could ty sticking a hose connected to the mains down the open vent and seeing if you can blast the airlock out. Similarly, if the heat exchanger has a drain point you might like to use this in the same way.

You could try loosening the return connection to the cylinder and seeing if you can bleed it - be v careful though, you might end up wrecking the cylinder if it's an old one.

You could also try just leaving it for a day or two and hope that the problem sorts itself out.