CH drain valves

17 Apr 2007
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United Kingdom
I'm on draining the system and it seems the downstairs rads are all fed from vertical pipes from above since the all have drain valves fitted. I got a radiator key from Screwfix buts its a slack on the drain valves and can't loosen one valve. Is there a better key to be had?


Also, have a drain valve on the pipework that feeds two conservatory rads but when I open the valve there's only a drip so is there a way unblock the valve or will I have to fit one of these to the rad?

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They usually need a Lockshield valve key -


The drain valve rubber seal will be stuck to the seat, take the valve stem out and pop in a small screwdriver and lever the seal out, be ready for the gush of water.
There isnt much you can do to conservatory drain ,it looks too close to the floor. The rubber seal in those tends to go block the thing up,probably as the fitter soldered it without removing the seal first.
Or even loosen the valve right off without removing and get a small screwdriver into the drain spout and lever the seal down off the seat, if it's melted though it may not seal back up.
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As above, but I often use a screw which I twist in the hole and then pull use that to pull the washer out. Be advised that you might need a new washer.

I am not a plumber but when dealing with drain off valves, I buy a like for like replacement and use the washer from that. Not the cheapest way to do it though. Someone here however recommend smearing a little bit of silicone grease on to the washer to reduce the risk of it sticking in the first place.
Thanks All!

I managed to drain all but one rad off. For the two in the conservatory, I put a bowl underneath a rad pipe and loosened the compression joint.

The water was clean that came out but will fill adding 0.5L cleaner, run then drain again, adding anti-corrosion although it may be wise to an intermediate drain and fill with only water to get most of the cleaner flushed out as much as I can.
I use bin bags to drain rads. The bag is thin enough to slide up over the rad nut, if you tuck the bag up behind the rad, it will easily hold 5L. With larger rads, I use two or more bags. I don't trust the cheaper bin bags with more than 5L.
I've run the CH and although all rads have been bled, some are not getting warm so it seems the valves are stuck shut even though I've set the thermostat valves to 2.

One rad is getting lukewarm but one pipe connection is cold while the other side is warm. The bother is, that's the one I put the cleaner in so it ain't going to circulate till I get the stuck shut valve open.
Did all your rads heat up well before you drained down ?
What was the reason for draining the system ?
TRV's sometimes get stuck in closed position. Remove the actuator head ,and check the pin in the valve body moves freely up and down a few millimetres.
I moved into the house earlier this year and so far have only used the Vaillant combi boiler for HW.
I thought it best to drain the CH and refill with cleaner to flush the system clean.
The rad getting lukewarm is the only one without a TRV.



I also have two rads not getting heat from either side, both have TRVs.
Close every other radiator down ,by their TRV ,see if the one without TRV now heats up fully.
Later on you can check the TRV pins are free in the two rads that don't heat.
I'm making progress.

I took the TRVs off and checked the pins. All operating.

I now have heat at radiators that were cold but I'm going to fit a TRV to the rad, shown above, that hasn't got one. I presume the 10mm versions sold at SF are suitable. Its a Myson rad.

Regarding the anti-frost setting on the TRV, I presume that lets a trickle through?
There may be a reason that one radiator was not fitted with a TRV , may be best left as it is.
Frost setting on TRV will make the valve open if temperature drops to a certain low level.
There may be a reason that one radiator was not fitted with a TRV , may be best left as it is.

I've looked into this and it seems it could be a by-pass rad. If all other rads are closed, the boiler pump doesn't burn out if the CH is switched on.

All rads are now heating so I'll leave the cleaner in for a week, then drain and refill adding anti-corrosion.
Really depends on the boiler and whether it has an internal bypass, that being said never a bad idea to have a rad that allows flow through the boiler, as long as it's never turned off, that's why there should really be 2 lockshields to make it tamper resistant.

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