DIY Doctor

Could gunk in expansion tank cause damage to central heating?

Postby dpw_ » Sun Oct 11, 2020 7:22 pm

Hi - DIY plumber looking for advice.

We have what I think is a Y-plan system, where a single boiler heats the hot water tank and the radiators.

This morning I fitted a new radiator. simple enough, no leaks yet...

Tonight I noticed the CH and water pump was making a terrible noise, and the rads were cold despite the stat demanding heat. I tapped the pipes around the pump, and they sounded empty, and the bleed valve by the hot water tank was not pressurised when I checked there.

I guess that filling the new radiator caused a massive airlock, although where the air came from I have no idea.

The expansion tank in the loft was full of black water, with lots of big globs of gunk. Really gross, like a fish tank overgrown with pond weed.

Despite the gagging, I emptied the expansion tank via a bucket and down the loo, and when I could access the pipe feeding the system, I gave it a 'good fingering' as a make shift plunger. This seemed to release a blockage in the pipework below (judging by the gurgling). I then cleaned the tank and refilled.

The system seems to be working now but I am worried that I have a glob of gunk in the system which will cause an issue down the line.

Do I need to do anything?

Over time we intend to replace a number of rads, I will be cleaning out the expansion tank first next time

Thanks for any advice.

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Simply Build It

Postby stoneyboy » Tue Oct 13, 2020 9:52 pm

Hi dpw_
Suggest you should flush the system, fit a filter (magnatec or something similar) and add system preservative when refilling.
Regards S
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