Drain tap leaks when in use.

[Bordonbert]

Hi guys.

This should be very simple for you knowledgeable types in here. I have a simple CH system on two floors with only two radiators on the ground floor fed from a single feed up above to suit our concrete floor. It's a really convenient system to work on except for one thing. The drain tap is fitted on the bottom horizontal return from one leg of a radiator at its absolute lowest point on the ground floor in a very convenient place but, when I come to use it, it leaks! When I say leaks I mean it is a constant dribble. It is sound as a bell when it is locked up and not actually in use but when I open it to release water into the hose it comes out through the correct spigot but it also dribbles out of the control screw in line with the fitting. (Hope that is clear enough. Just in case I have attached a pic showing where I mean it leaks from.)

Is this normal for a simple brass fitting of this type? I would have thought that that is the one thing a good design would have prevented so I am leaning towards it being faulty. It means that at the moment we have to drain through a hose on the outlet spigot and also constantly catch and empty the considerable amount of water which leaks from the square headed control cap at the same time.

 

[Gasmk1]

no they quite often do that you have to get them just right when drawing or just put a bowl under, next time you drain down change it for one like this Drain Cock 15mm - https://www.NoLinkingToThis/p/drain-cock-15mm/99939?tc=JT7&ds_kid=92700055281954514&ds_rl=1249404&gclid=Cj0KCQiA7NKBBhDBARIsAHbXCB6Pj_n3_-XRtpOWREb_tHFvrcpI-wjvfJMpCP40aF2-wOquoy5CynEaAmy0EALw_wcB&gclsrc=aw.ds

 

[Keefy]

That's a Type B drain cock. I find Type A to be the better option because they're less likely to give you the problem you describe. I'd personally change it if it bothers you that much.

Edit: Gasmk1 beat me to it.

 

[Bordonbert]

Haha! I was looking at the exact same item 99939 in Screwfix online when you posted Gasmk1. I've got you Keefy, that is the Type A and Type B difference explained to me. The "head" for want of a better word is made with internal glands to reduce leakage. It seem odd to me that any design for this type of job would be allowed to leak straight past the threads but hey, I'm no plumbing design engineer. Thanks both of you for the advice, it's appreciated. With Screwfix only a quarter of a mile away from the house I'll get a new one in tomorrow.

 

[Bordonbert]

Job done! CH system drained, cleaned out, refilled with Fernox without any traumatic incident. Jeez, the amount of crap that was in the header tank had to be seen to be believed. There was a layer of black CuO in the bottom, gobs of what looked like rust, and a thick oily scum across the whole surface. To my layman's eyes, boy did it need doing. It took three "fill to the outlet and clean" operations to get the majority of it out. I know that is pedantic but when you are in your own home and not against the clock as in a tradesman it makes sense to be overly fussy.

The drain cock wasn't a problem in use while draining, but it was a good job I decided to break it down to check it out anyway. When I came to remove the capsule, the "thumbscrew" part was sensibly tight so it loosened and screwed out easily but the square shaft then came out leaving the washer behind. After a bit of very gentle probing with a thin screwdriver this eventually came out in two pieces. It had gone from rubber to stiff plastic and just crumbled across. It was also now not a plain washer but was in kind of a "T" cross section having been forced so far inside its mating flange in the tap body by the tight screw pressure. It must have been tightened to within an inch of its life. I have always worked to finger tight then just nip around a quarter turn which is working fine at the moment. I'm assuming that would be alright?

That washer was easy to renew but the O-ring was not. Our local plumbers merchants, usually pretty comprehensive, did not carry a small enough size. I even tried to buy a new drain cock and use the whole inner setup transplanted into my existing body. No go! The main body threads were different. Fortunately, with their agreement I had tested before buying. It is worth remembering that these are not all interchangeable in future. I ended up adding a turn or two of PTFE tape around the overall thumbscrew to main body thread and just holding onto the original O ring on the inner shaft/ That had done its job during the drain. Not perfect but working and it is easy enough to address if I can get the right one.

Anyway, thanks for the heads up guys. It's a simple job to do but it helps to know the parts and the correct way of setting them up and you pointed me at that.