Banging boiler after refilling system.

I have a gloworm 50 fuelsaver boiler - part of a pumped central heating system. I\\\'ve just drained my syystem and rerouted some pipes. after curing some leaks I bled the radiators and set the pump running (boiler off). I heard gurgling for a while then it went pretty queit. I then assumed there was no air left in the system and so lit the boiler. Lots of gurgling started again (with some banging in the boiler), the boiler got very hot and the overheat stat shut it down. THis sounds like air in the boiler to me (or sludge). I cant see a bleed valve like on the radiators. There\\\'s a drain point though. One thing I did which I\\\'ve now found out was wrong was that I bled the upstairs radiators first. Might this have caused the problem. I\\\'m thinking of draining the whole system again, opening the boiler drain port to clear out any sludge etc. Is this the best thing to do or do any of you experts have a better idea of how I can cure this problem. Help would be gratefully apprciated cos its freezing and I\\\'m getting a bit of stick from the family now !!! Cheers Tony

What's wrong with bleeding upstairs rads first? I do!

Draining if you think you've got sludge is not a bad idea. Though it sounds like air, not sludge.

Air should be able to get out of your boiler even if it has no bleed valve. In fact, especially if you have no bleed valve.

Turn pump off, bleed rads (I'd do upstairs first), and find any other bleed points on your pipe work. There may be more than you think, hidden under insulation. Run pump until gurgling stops, bleed rads. Run pump 'til gurgling stops, bleed rads.......

Thanks for the advice but after leaving the pump running for an hour and then lighting it, everything ok. I now have a new problem - I've rerouted some pipes and now my upstairs radiators are fine but there is no heat at all from my down radiators. If i turn off a rad upstairs the heat travels further down the pipe so I think I've got a flow problem. To prove a point I've put the system back (nearly) as it was to see if the problem would clear but another (unconnected ?) problme has now occurred - my pump has packed up (it was squaling) I've opened it and found that the drive has sheared off. I'm going to get another pump now but does anyone know if there should be problems such as no downstairs heat just because I've rerouted some pipes. I'm hoping that my pump was on its last legs and so wasn't creating enough flow to pass the water along a 1m length of pipe before it went down from the loft. In my new layout I've added about 5 more 90 degree bends. Is this likely to cause reduced flow problems. I'm hoping that my new pump will cure all but any advice would be appreicated.

Thanks for the advice but after leaving the pump running for an hour and then lighting it, everything ok. I now have a new problem - I've rerouted some pipes and now my upstairs radiators are fine but there is no heat at all from my down radiators. If i turn off a rad upstairs the heat travels further down the pipe so I think I've got a flow problem. To prove a point I've put the system back (nearly) as it was to see if the problem would clear but another (unconnected ?) problme has now occurred - my pump has packed up (it was squaling) I've opened it and found that the drive has sheared off. I'm going to get another pump now but does anyone know if there should be problems such as no downstairs heat just because I've rerouted some pipes. I'm hoping that my pump was on its last legs and so wasn't creating enough flow to pass the water along a 1m length of pipe before it went down from the loft. In my new layout I've added about 5 more 90 degree bends. Is this likely to cause reduced flow problems. I'm hoping that my new pump will cure all but any advice would be appreicated.

Unless you seriously screwed up the pipe layout the problem could have been a balancing issue - rad valves near the pump only need to be 1/4 turn or so open (lockshield valves I mean) so the rest of the system gets enough flow. Air locks are common to specific bits of ch system, clear by closing all the rads which DO work.

Critical bleed point often missed can be on the pipes which go into the HW cylinder (from the boiler).