Is my boiler blocked?

[rabgirl]

I have an elderly (20yr) Ideal Classic boiler with an open vent system, 5 rads and 2 heated towel rails. Boiler is serviced regularly and advised is still going strong. Last week we upgraded the rads, flushed the system and added inhibitor. However. The cold feed pipe in the loft gets warm, and flows into the vent tank when the boiler is running at the normal temp - it is fine when the boiler is switched off and just the pump is running; it is fine when the boiler is on really low - it's just when I turn it up to the middle temp, it starts to flow over. Is there a blockage in the boiler flow?

I wanted to isolate the boiler, drain it off with the local drain valve and unblock it with a hose feed into the drainoff, but nothing comes out of the valve. Is there a blockage somewhere with old sludge etc? Can I unblock it some other way? I have tried using a magnet against the return/flow pipes above the boiler, to try and locate a sludge blockage, but found nothing.

Help and advice greatly appreciated!

 

[Agile]

It will be likely to be blockages around where the feed and vent pipes join the system.

Usually need to be cut out and mechanically cleaned out. Only HCl usually dissolves this dirt and its unsafe to put that into a system.

Tony

 

[rabgirl]

It will be likely to be blockages around where the feed and vent pipes join the system.

Do I need to look at the pipework right from where the pipes enter the boiler, back up into the loft?

Thanks

 

[Agile]

Usually within 300 mm of where I described.

Check with your magnet.

Read about it in the FAQ on this site.

Tony