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How to drain old combi boiler which also has an expansion tank to fit new heated towel rail

Postby Niko » Fri Aug 18, 2017 4:50 pm


Hi All.

First time on this forum, and first time home-owner too.

I've got a couple of plumbing jobs to do (never attempted any before but know one end of a screwdriver from the other) - but I appear to have a weird hybrid boiler in this place (Worcester Bosch Highflow 3.5) which has a small expansion / header tank in the loft. Pipework to the rads is 8mm microbore.

First job is to replace an old rad with a towel rail. I've been researching how to drain down heating sytems, and I think I've managed to locate the drain valve on the bottom of the boiler (see pics) rather than on a rad.

I'm wondering whether I just need to attach a hose to the drain on the boiler, turn off the water to the header tank (which I think I've located on the feed pipe), and open the bleed valves on the rads from top to bottom?

I'm also guessing that once the system is drained, I can close the bleed valves on the rads and refill from the header tank, then fire the boiler back up? There's no sign of a pressure valve / readout - so presume that it's gravity fed from the header tank in the loft?

I'm not 100% sure that the drain valve I've located on the boiler is the right one, and it (boiler) also seems to have a couple of expansion tank type things in the boiler itself (coated in silver insulation in pic) - scuse my ignorance.

I'm also a little concerned at the state of the water and interior of the expansion tank, which looks very rusty - I've also got very sluggish flow to another rad (which is the next project) and don't want to flush through rubbish into other rads.

Any help on the correct procedure would be much appreciated.

Thanks in advance!

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