Water in expansion tank but not refilling

[Dave Morris]

Hi. My central heating system is 15 years old and I have recently had the system flushed to try and rectify the following problem. It is not a combi and comprises of a downstairs boiler, with a HW tank, pump and motorised valve in a 1st floor airing cupboard with a header tank in the loft. The system will run trouble free for 2 to 3 weeks then all of a sudden the pipes and boiler make an incredible banging noise and the system dumps loads of water into the expansion tank but does not take any back into the system. when I try to bleed the upstairs radiators I get a little bit of air out then nothing at all. It air locks. when I finally remove the air locks by filling from the down stairs up etc, the system will work fine for another few weeks.

HELP

Dave

 

[ChrisR]

The feed and expansion pipe (the 15mm one) is blocked with hard scale at its base, where it meets the circuit. Cut out a few feet of pipe and renew it.

If that means rebuilding the house there may be options. What boiler do you have? Yours obviously does boile - so I guess it's old. Flushing doesn't usually clear the hard stuff.

 

[Dave Morris]

Thanks chris. I shall give that a go tommorrow.

 

[oilman]

It could be hard scale as ChrisR says, and it may be debris accumulated at the T joint, or at the last bend before the T. Why it collects here I don't know. So if you cut the pipe and shove something up it, you may clear it.