Boiler cut out after part system flush

[DCA]

I have a Glowworm Fuelsaver F boiler running an 11 radiator microbore system which is 20 years old.
For some months, the boiler has been making kettleing(?) noises on and off and none of the ground floor radiators will now heat up at all.
Having done a bit of research, mostly on this site, and spoken to people wiser than me in such matters, I am led to believe the system might be sludged up, so this morning, I drained quite a bit of water from the system (water was all clear), added a litre of Sentinel x400, refilled and switched everything back on. Expansion tank full, pump working fine, all radiators bled and air released from the air vent in the airing cupboard. BUT.......
when I switch on the boiler, it starts up fine but after 15 - 20 seconds it starts making bubbling noises and sounds as though something is being dragged inside the flow (I think) pipe coming out the top of the boiler. This happens whatever setting the boiler thermostat is set on.
My first thoughts are (1) is there an air lock in the boiler, and if so how do I get it out? (2) have I dislodged some sludge, which may have moved into the boiler, in which case do I just have to let the X400 run round the system for a few hours/days/weeks to clear it, or (3) have I completely bu**ered the system up and now need to call out a professional?
Sorry to go on so long for a first posting, but if I cant get some heat back in the house by tonight, my life won't be worth living!!!
Any suggestions gratefully appreciated.

 

[ChrisR]

Well if it isn't cancer or a heart attack it may as well be sludge in microbore heating which takes you out.

You may just have an air lock; search on that and you'll find out how it's possible but hard to backfill throuh a drain cock etc.

Or you may have dusturbed enough sludge to block things up to the point where you get no useful circulation. X400 is pretty mild, and won't dissolve your troubles away. DS40 might, but you'll either have to climb a steep learning curve or get someone in. Some mains flushing attempts would be worth a punt first - see the FAQ section.

 

[DCA]

Thanks for the advice Chris.

I have spent all weekend playing around with the system to no avail. However, I have discovered that before the boiler cuts out the return pipe into the boiler gets very hot first and then the flow pipe heats up. It takes some minutes for the heat to reach the the pipe going into the pump even when the pump is set on maximum (3).

Also before the boiler cuts off, I get the sound of boiling or bubbling water and an intermitant "slurping" sound like you get when you first turn the taps on after the main tank has been drained. When the boiler cuts out it then sounds as though water is draining back down the flow pipe back into the boiler. Sometimes there are also some loud clicks or bangs!

The pump seems to be working fine as I can hear water moving in the pipes, including the return pipe into the boiler, and I get a fine jet of water out of the radiators when I open the rad air valve.

I have now given up for the day! I propose to leave the x400 to do its work until next weekend and I will have another go at switching on the boiler and see what happens.

If it is a blockage is there anything better than x400 anyone can recommend to loosen the crud before powerjetting. If it is an air lock, how do I free it as I could not find anything to help on this forum? {Presumably this would also be cleared by a powerjet? Any suggestions gratefully received (including "give up and call a plumber!)

On a final note, just out of interest, what is the little round thing about the size and shape of a small baked bean tin, which sits in the pipe work just before the pump. It has the pipe from the boiler (I think) coming in one side, an overflow pipe coming out the top and a pipe to the pump the other side. Is there anything in this which could be causing a problem?

Thanks for reading this. They say a problem shared is a problem halved!!!