Draining down C/H system - radiators have stopped emptying


19 Apr 2006
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United Kingdom
We have put a cleanser in the radiator system and have come today to drain it out. The upstairs radiators drained but then the draining stopped and the downstairs radiators are still full. We have put the mains back on to see if this helps, but is has not.

We ahve a gravity feed system with a header tank in the loft and a biler downstairs. The water drains out of a tap in the boiler.

Any suggestions gratefully recieved - its freezing!

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is the boiler drain point higher than the rads? if not its possible the circuit for the downstairs rads drops from upstairs, requiring a hose to be connected to the rads downstairs.
Thanks Rob
The drain point is about the same level.
How would I go about attaching a hose to the downstairs rads?
presumably if the circuit is on a drop then a drain cock should be installed somewhere to drain the rads. usually under one of the rad valves but could be sticking through wall outside, could even be under the floor!

im assuming that you noticed the rads were still full when you tried to vent them?
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We are using what we think is a drain cock on the boiler, we haven't seen any other drain cocks obvious.

When we try to vent the rads, there does seem to be water in the rads.downstairs The mains appears to be flowing from the loft and is running out of the drain cock, as when the mains is turned off, the water from the drain cock slows and eventually stops. The water coming from the drain cock is dirty.
As rob884 has said your downstairs rads are probably fed from above (follow pipework, does it go up ?) if they have no draincock you will have to close both valves undo the 2 nuts closest to the rads stick your thumb over one end get someone else to do the same at the other end, carry the rad outside and empty it. Also a good time to flush it out with a hosepipe. Put plenty of dust sheets down because it can get messy.
Hi thanks for the advice.

What about the cleanser that may still be in the system. If we drain that rad, is there a way that we can flush the rest of the system to get rid of the rest of the cleanser. Will this work with running the mains through the system.
Undo the rad valves connections, they'll empty pdq!
If you do the same to all the downstairs rads you will remove most of the cleaner, you will then need to add some inhibitor (X100 etc) to keep it clean
If you are loosening off the downstairs rad valves to drain them (beware of gushing water!) it is worth fitting these valves with drain-off to replace the old ones. They are tremendously useful for doing an easy clean drain. They cost a few pounds each.

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